MicroCT analysis of hydroxyapatite bone repair scaffolds created via three-dimensional printing for evaluating the effects of scaffold architecture on bone ingrowth

Recent studies have shown that it is now possible to construct tissue-engineered bone repair scaffolds with tight pore size distributions and controlled geometries using 3-D Printing techniques (3DP). This study evaluated two hydroxyapatite (HA) 8-mm diameter discs with controlled architectures in a rabbit trephine defect at 8 and 16 weeks using a 2 x 2 factorial design. Input parameters were time and scaffold void volume at two levels. Three output variables were extracted from MicroCT data: bone volume ingrowth with respect to total region of interest, bone volume ingrowth with respect to available ingrowth volume, and soft tissue volume. The experiment measured two groups--Group 1: 500-microm x 500-microm channels parallel to the scaffold's long axis and penetrating up 3-mm from the bottom. Group 2: 800-microm x 800-microm struts spaced 500 microm apart set perpendicularly to each other in each printed layer. Rendered 3-dimensional MicroCT scans and undecalcified histological slides of implants revealed good integration with the surrounding tissue, and a sizeable amount of bone ingrowth into the device. Factorial analysis revealed that the effects of time were the greatest determinant of soft tissue ingrowth, while time and its interaction with void volume were the greatest determinants of bone volume ingrowth with respect to both total and available volume.

In vivo bone response to 3D periodic hydroxyapatite scaffolds assembled by direct ink writing

The in vivo bone response of 3D periodic hydroxyapatite (HA) scaffolds is investigated. Two groups of HA scaffolds (11 mm diameter x 3.5 mm thick) are fabricated by direct-write assembly of a concentrated HA ink. The scaffolds consist of cylindrical rods periodically arranged into four quadrants with varying separation distances between rods. In the first group, HA rods (250 microm in diameter) are patterned to create pore channels, whose areal dimensions are 250 x 250 microm(2) in quadrant 1, 250 x 500 microm(2) in quadrants 2 and 4, and 500 x 500 microm(2) in quadrant 3. In the second group, HA rods (400 microm in diameter) are patterned to create pore channels, whose areal dimensions of 500 x 500 microm(2) in quadrant 1, 500 x 750 microm(2) in quadrants 2 and 4, and 750 x 750 microm(2) in quadrant 3. Each group of scaffolds is partially densified by sintering at 1200 degrees C prior to being implanted bilaterally in trephine defects of skeletally mature New Zealand White rabbits. Their tissue response is evaluated at 8 and 16 weeks using micro-computed tomography, histology, and scanning electron microscopy. New trabecular bone is conducted rapidly and efficiently across substantial distances within these patterned 3D HA scaffolds. Our observations suggest that HA rods are first coated with a layer of new bone followed by subsequent scaffold infilling via outward and inward radial growth of the coated regions. Direct-write assembly of 3D periodic scaffolds composed of micro-porous HA rods arrayed to produce macro-pores that are size-matched to trabecular bone may represent an optimal strategy for bone repair and replacement structures.

Age, temperature, and parasitaemia predict chloroquine treatment failure and anaemia in children with uncomplicated Plasmodium falciparum malaria

The prevalence of chloroquine-resistant Plasmodium falciparum malaria has been increasing in sub-Saharan Africa and parts of South America over the last 2 decades, and has been associated with increased anaemia-associated morbidity and higher mortality rates. Prospectively collected clinical and parasitological data from a multicentre study of 788 children aged 6-59 months with uncomplicated P. falciparum malaria were analysed in order to identify risk factors for chloroquine treatment failure and to assess its impact on anaemia after therapy. The proportion of chloroquine treatment failures (combined early and late treatment failures) was higher in the central-eastern African countries (Tanzania, 53%; Uganda, 80%; Zambia, 57%) and Ecuador (54%) than in Ghana (36%). Using logistic regression, predictors of early treatment failure included younger age, higher baseline temperature, and greater levels of parasitaemia. We conclude that younger age, higher initial temperature, and higher baseline parasitaemia predict early treatment failure and a higher probability of worsening anaemia between admission and days 7 or 14 post-treatment.

Performance of hydroxyapatite bone repair scaffolds created via three-dimensional fabrication techniques

The current study analyzes the in vivo performance of porous sintered hydroxyapatite (HA) bone repair scaffolds fabricated using the TheriForm solid freeform fabrication process. Porous HA scaffolds with engineered macroscopic channels had a significantly higher percentage of new bone area compared with porous HA scaffolds without channels in a rabbit calvarial defect model at an 8-week time point. An unexpected finding was the unusually large amount of new bone within the base material structure, which contained pores less than 20 microm in size. Compared with composite scaffolds of 80% polylactic-co-glycolic acid and 20% beta-tricalcium phosphate with the same macroscopic architecture as evaluated in a previous study, the porous HA scaffolds with channels had a significantly higher percentage of new bone area. Therefore, the current study indicates that scaffold geometry, as determined by the fabrication process, can enhance the ability of a ceramic material to accelerate healing of calvarial defects.

Performance of degradable composite bone repair products made via three-dimensional fabrication techniques

This study analyzed the in vivo performance of composite degradable bone repair products fabricated using the TheriForm process, a solid freeform fabrication (SFF) technique, in a rabbit calvarial defect model at 8 weeks. Scaffolds were composed of polylactic-co-glycolic acid (PLGA) polymer with 20% w/w beta-tricalcium phosphate (beta-TCP) ceramic with engineered macroscopic channels, a controlled porosity gradient, and a controlled pore size for promotion of new bone ingrowth. Scaffolds with engineered macroscopic channels and a porosity gradient had higher percentages of new bone area compared to scaffolds without engineered channels. These scaffolds also had higher percentages of new bone area compared to unfilled control defects, suggesting that scaffold material and design combinations could be tailored to facilitate filling of bony defects. This proof-of-concept study demonstrated that channel size, porosity, and pore size can be controlled and used to influence new bone formation and calvarial defect healing.

Engineered cellular response to scaffold architecture in a rabbit trephine defect

Tight control of pore architecture in porous scaffolds for bone repair is critical for a fully elucidated tissue response. Solid freeform fabrication (SFF) enables construction of scaffolds with tightly controlled pore architecture. Four types of porous scaffolds were constructed using SFF and evaluated in an 8-mm rabbit trephine defect at 8 and 16 weeks (n = 6): a lactide/glycolide (50:50) copolymer scaffold with 20% w/w tri-calcium phosphate and random porous architecture (Group 1); another identical design made from poly(desaminotyrosyl-tyrosine ethyl ester carbonate) [poly(DTE carbonate)], a tyrosine-derived pseudo-polyamino acid (Group 2); and two poly(DTE carbonate) scaffolds containing 500 microm pores separated by 500-microm thick walls, one type with solid walls (Group 3), and one type with microporous walls (Group 4). A commercially available coralline scaffold (Interpore) with a 486-microm average pore size and empty defects were used as controls. There was no significant difference in the overall amount of bone ingrowth in any of the devices, as found by radiographic analysis, but patterns of bone formation matched the morphology of the scaffold. These results suggest that controlled scaffold architecture can be superimposed on biomaterial composition to design and construct scaffolds with improved fill time.

Kinetic analysis of growth and xanthan gum production with Xanthomonas campestris on sucrose, using sequentially consumed nitrogen sources

A batch fermentation strategy using Xanthomonas campestris ATCC 13951 for xanthan gum production has been established in which all essential medium components are supplied at the onset. This has been achieved using sucrose as sole sugar feedstock. Sequential consumption of nitrogen sources (soybean hydrolysates, ammonium and nitrate salts) was observed to facilitate the further optimisation of the medium. Biomass accumulation was limited by phosphate availability. Xanthan yields of more than 60% (grams of xanthan per gram of sugar) have been obtained with constant acetyl content. However, pyruvyl substitution decreased as the growth rate declined, due to the metabolic constraints specific to phosphate depletion. High rates of carbon conversion into xanthan were observed throughout the culture and the ATP/ADP ratio was not affected by the decline in the specific growth rate.

Final report of the FOPE II Pediatric Generalists of the Future Workgroup

The Future of Pediatric Education II (FOPE II) Project was a 3-year, grant-funded initiative, which continued the work begun by the 1978 Task Force on the Future of Pediatric Education. Its primary goal was to proactively provide direction for pediatric education for the 21st century. To achieve this goal, 5 topic-specific workgroups were formed: 1) the Pediatric Generalists of the Future Workgroup, 2) the Pediatric Specialists of the Future Workgroup, 3) the Pediatric Workforce Workgroup, 4) the Financing of Pediatric Education Workgroup, and 5) the Education of the Pediatrician Workgroup. The FOPE II Final Report was recently published as a supplement to Pediatrics (The Future of Pediatric Education II: organizing pediatric education to meet the needs of infants, children, adolescents, and young adults in the 21st century. Pediatrics. 2000;105(suppl):161-212). It is also available on the project web site at: This report reflects the deliberations and recommendations of the Pediatric Generalists of the Future Workgroup of the Task Force on FOPE II. The report looks at 5 factors that have led to changes in child health needs and pediatric practice over the last 2 decades. The report then presents a vision for the role and scope of the pediatrician of the future and the core attributes, skills, and competencies pediatricians caring for infants, children, adolescents, and young adults will need in the 21st century. Pediatrics 2000;106(suppl):1199-1223; pediatrics, medical education, children, adolescents, health care delivery.

Final report of the FOPE II Financing of Pediatric Education Workgroup

Some of the challenges of financing pediatric medical education are shared with all medical education; others are specific to pediatrics. The general disadvantage that funding of graduate medical education (GME) is linked to reimbursement for clinical care has uniquely negative consequences for freestanding children's hospitals because they therefore receive little Medicare GME support. This represents both a competitive disadvantage for such hospitals and an aggregate federal underinvestment in children's health care that now amounts to billions of dollars. The need to subsidize medical student and subspecialty education with clinical practice revenue jeopardizes both activities in pediatric departments already burdened by inadequate reimbursement for children's health care and the extra costs of ambulatory care. The challenges of funding are complicated by rising costs as curriculum expands and clinical education moves to ambulatory settings. Controversies over prioritization of resources are inevitable. Solutions require specification of costs of education and a durable mechanism for building consensus within the pediatric community. Pediatrics 2000;106(suppl):1256-1269; medical student education, continuing medical education, medical subspecialties, children, pediatrics, health maintenance organizations, managed care, hospital finances, children's hospitals.

Final report of the FOPE II Education of the Pediatrician Workgroup

This report from the FOPE II Education of the Pediatrician Workgroup assesses the current status and future trends of pediatric education. The attributes of each level of the education process (undergraduate, residency, fellowship, continuing medical education [CME]) are considered within the framework of lifelong learning. The pediatric education of nonpediatrician providers is carefully considered. The Workgroup proposes and describes a new model for pediatric education that encompasses educational needs assessment, curriculum development and outcomes evaluation. Particular attention is paid to CME, with a review of the strengths and problems of the current system. The proposal for improving CME in the 21st century highlights the need for each pediatrician to have a "CME home," and several models and scenarios are explored. Appendices summarize the results of several surveys conducted on behalf of the Workgroup, and list societal trends and advances in pediatric health care that will influence pediatric education in the future. Pediatrics 2000;106(suppl):1175-1198; pediatric education, educational needs assessment, curriculum development, outcomes evaluation.

Final report of the FOPE II Pediatric Workforce Workgroup

From the inception of the Future of Pediatric Education II (FOPE II) Project, it was acknowledged that any discussion of pediatric education would need to encompass a review of the pediatric workforce. This report looks at the current trends in pediatric workforce and draws some conclusions regarding future growth and composition. In addition to looking at demographic trends, ranging from geography to gender, the report explores influences including managed care, telemedicine, and others. Models for determining workforce needs are described and scenarios and projections are discussed. Pediatrics 2000;106(suppl):1245-1255; pediatric workforce.

Final report of the FOPE II Pediatric Subspecialists of the Future Workgroup

The report of the Pediatric Subspecialists of the Future Workgroup of the Second Task Force on Pediatric Education reviews the critical changes of the past 2 decades that have affected the provision of pediatric subspecialty services, education of pediatric health care providers, and the acquisition and application of new knowledge. The report considers the future needs that will determine the ability of pediatric subspecialists to meet identified goals. Recommendations for change in the education, role, and financing of the pediatric subspecialist are reported together with those of other workgroups. Pediatrics 2000;106(suppl):1224-1244; pediatric subspecialist, pediatric subspecialist workforce, education pediatric subspecialist, research pediatric subspecialist.

Evolution of poecilogony and the biogeography of North American populations of the polychaete Streblospio

Invertebrate interspecific developmental patterns can be highly variable and, taxonomically, are considered only weakly constrained. Intraspecifically, some invertebrate species possess multiple developmental modes-a condition known as poecilogony. Closer examination of most putative poecilogenous species, however, has not supported poecilogony, but rather has uncovered hidden or cryptic species. The polychaete Streblospio benedicti is a well-known, poecilogenous species found along the coast of North America. We collected mitochondrial cytochrome subunit I DNA sequence data from 88 individuals taken from 11 locations along the Atlantic, Gulf, and Pacific Coasts of the United States to provide a phylogenetic framework from which to interpret intraspecific variation in larval life history and brooding structure morphology in this species. Our results are consistent with a recent revision of the species into two separate species: S. benedicti, a pouched brooding form distributed along the Atlantic and Pacific Coasts, and S. gynobranchiata, a branchiate brooding form in the Gulf of Mexico. Contrary to the redescription, S. benedicti is paraphyletic because the pouched brooding population in Vero Beach, Florida shows strong genetic affinity with Gulf of Mexico populations (S. gynobranchiata). However, S. benedicti is a true poecilogenous species, with both lecithotrophic and planktotrophic individuals possessing identical mitochondrial DNA haplotypes. Crossbreeding experiments further support the molecular phylogeny with reproductive isolation demonstrated between, but not within, the major phylogenetic clades consistent with the previously described species. The genetic break near Vero Beach, Florida, corresponds to a well-known phylogeographic boundary, but the estimated time of separation for the Streblospio spp., approximately 10 million years before present, predates all other known phylogeographic subdivisions in this area. This suggests that biogeographic sundering in this region is a recurrent event. Divergence times within the major Streblospio spp. clades are recent and indicate that changes in larval life history as well as brooding structure morphology are highly plastic and can evolve rapidly.

Five- to fifteen-year follow-up of fresh autologous pericardial valved conduits

OBJECTIVE

Evaluate long-term results of autologous pericardial valved conduits in the pulmonary outflow.

METHODS

Between June 1983 and October 1993, 82 conduits were placed in the outflow of the venous ventricle. Patients who received homografts (n = 2 patients), heterografts (n = 3 patients), and valveless conduits (n = 19 patients) and those patients who died within 90 days after the operation were excluded. Fifty-four survivors of pulmonary outflow reconstruction with fresh autologous pericardial valved conduits were followed up from 5 to 15 years (mean, 7.47 +/- 2.8 years). Diagnosis include d -transposition of great arteries (n = 16 patients), L -transposition of great arteries (n = 14 patients), tetralogy of Fallot, pulmonary atresia with ventricular septal defect (n = 11 patients), truncus arteriosus (n = 10 patients), and double-outlet ventricle (n = 3 patients). Implantation age ranged from 0.25 to 24 years (mean, 5.2 +/- 4.2 years). Median conduit diameter was 16 mm. Two-dimensional echocardiographic Doppler evaluations were made yearly; 9 patients underwent cardiac catheterization. Reintervention for stenosis was indicated when the pressure gradient exceeded 50 mm Hg.

RESULTS

Three late deaths were unrelated to the conduit. Thirty-five autologous pericardial valved conduits increased in diameter (1-7 mm), remained unchanged in 15 patients, and reduced 1 to 2 mm in 4 patients. The median diameter was 18 mm at the last evaluation (P =.0001). Eight patients required conduit-related reoperation 3 to 8 years after the implantation. Two patients underwent balloon dilation of the autologous pericardial valved conduit. No conduit had to be replaced. Freedom from reintervention at 5 and 10 years was 92% and 76%, being 100% at 10 years for conduits larger than 16 mm at time of implantation.

CONCLUSIONS

Autologous pericardial valved conduits show excellent long-term results and compare favorably with other conduits.

Four comments on The Bell Curve

This paper first analyzes the central claim of the Bell Curve, to wit, that intelligence is declining in the United States. (Race is the inflammatory issue in the book, but is said to be only a side issue by the authors.) Part II of the paper then discusses how in principle one could determine whether race affects IQ, and how the difficulty of doing so in practice may explain the wildly different conclusions people arrive at in this area. Part III then points out how the assumption that the attribute under discussion is properly portrayed with a 'bell curve' itself is a misunderstanding; the Normal distribution is a sign that a piece of research has allowed for all the relevant variables, rather than a description of a characteristic as found in nature. And Part IV reminds us of how IQ test scores come to resemble a bell curve--entirely an artifact of the test makers.

Lysenkoism and the population control movement

The case of Lysenkoism in the Soviet Union helps us understand how people's wrong beliefs can be influenced by what the information they receive from outside, especially when there is a large volume of media coverage and there is no contrary information to be heard. The population control movement in contemporary United States has many parallels to the Lysenko episode.

Long-term follow-up of autologous pericardial valved conduits

BACKGROUND

The aim of this study was to evaluate the long-term results of the use of an autologous pericardial valved conduit in the outflow tract of the venous ventricle in congenital heart malformations.

METHODS

Fifty-one patients were followed up for a period of 12 to 120 months; 30 for more than 36 months and 13 for more than 72 months. All were evaluated clinically and by two-dimensional and Doppler echocardiography. Eight patients were recatheterized. Postoperative evaluation included serial measurement of pressure gradients and the conduit's diameter at the proximal, valvular, and distal levels. Reoperation because of stenosis was indicated when the gradient across the right ventricular outflow was greater than 50 mm Hg. The reoperation rate in relation with postoperative time, diameter of the autologous pericardial valved conduit at the time of implantation, and malformation was statistically analyzed.

RESULTS

In 27 patients the conduit increased its diameter 1 to 7 mm. In 20 patients the diameter remained unchanged, whereas a reduction was noted in 4. Conduit survival free of reoperation for the whole group was 89.9% at 5 years. Conduit survival free of reoperation was 100% at 5 and 7 years for conduits larger than 16 mm at the time of implantation. It was 95% (standard deviation = 4.8%) at 5 years and 72.3% at 7 years for those 16 mm or less. For patients operated after January 1, 1986 (technical modification), conduit survival free of reoperation was 95.4% at 7 years postoperatively.

CONCLUSIONS

These results compare favorably with those of other available conduits.

The new biostatistics of resampling

The statistical techniques reported in medical journals are often poorly understood and misused by researchers, and difficult for readers to comprehend. Even the relatively simple t test embodies an intricate collection of mathematical formulas such as the Normal approximation, with unintuitive elements such as pi and e. The researcher must consult a body of rules indicating whether a technique is applicable or inapplicable. If he or she does select a sound method and use it correctly, its mathematical complexity will still leave most readers in the dark. In most situations the resampling approach is at least as efficient as the formulaic method. It is transparently clear to the researcher and reader, and it protects the researcher from using the wrong formulaic technique. In this paper we will define the four steps in the resampling method, compare this procedure with standard formulaic treatment of the same data, and discuss the advantages of the resampling approach.

The effect of immigration on aggregate native unemployment: an across-city estimation

"This study investigates the relationship between the rate of immigration into various [U.S.] cities in various years and the level and change in unemployment. In pooled regressions, immigration lagged one year does not show a statistically significant effect either by itself or when other lags are added. Individual regressions using the difference in unemployment rates over time show a slight, but statistically insignificant, positive displacement effect over two-year periods. The evidence indicates that there is little or no observed increase in aggregate native unemployment due to immigration, even in the relatively short run during which adjustment frictions should be most severe."

Activation induced changes in expression and structure of the IL-7 receptor on human T cells

Activation of human peripheral blood T cells renders them capable of proliferating to IL-2, -4, and -7, and upregulates the receptors for IL-2 and -4. In this study the effect of activation on the receptor for IL-7 has been investigated. Scatchard analysis showed dual affinity binding of IL-7 to peripheral blood mononuclear cells (PBMC). Furthermore, activation of PBMC with anti-CD3 antibodies resulted in a 4-fold downregulation of both the high and low affinity IL-7 receptors. SDS-PAGE analysis of [125I]IL-7 cross-linked resting PBMC revealed a major complex of 104/107 kDa (reduced/non-reduced) and a minor complex of 184/178 kDa (reduced/non-reduced). In contrast, cross-linking of activated PBMC revealed a third prominent complex of 93 kDa (non-reduced) not seen on unstimulated cells. This 93 kDa complex was observed on purified activated peripheral blood T cells and T cell blasts. Moreover, on a panel of IL-7 responsive T cell clones the 93 kDa complex was the only major cross-linked product observed. These results demonstrate that T cell activation causes changes in both the level of expression of the IL-7 receptor and the nature of the proteins associated with the receptor. It is postulated that these changes in receptor structure may be related to the acquisition of responsiveness to the IL-7 growth signal.

Population growth, farmland, and the long-run standard of living

"This paper studies the natural-resources element in the theory of population growth over the very long run. In the context of the stock of land and Malthusian crises in earlier times, the model shows how resources have become more available rather than more scarce, even as population and income have increased. The paper sketches a mechanism which added to the Malthusian system, leads to entirely different conclusions than does the Malthusian system.... That is, population growth creates new problems which in the short run constitute additional burdens which, in the longer run, lead to new developments that leave people better off than if the problems had never arisen." This is a revised version of a paper originally presented at the 1989 Annual Meeting of the Population Association of America (see Population Index, Vol. 55, No. 3, Fall 1989, p. 382).

The Sperm Transfer System in Kinbergonuphis simoni (Polychaeta:Onuphidae)

Tube dwelling Kinbergonuphis simoni (Santos, Day and Rice) achieves a 98.9% fertilization efficiency by means of a sperm transfer system involving spermatophores and seminal receptacles. The spermatophores are mushroom-shaped structures released as clumps. The seminal receptacles are paired sac-like organs embedded in the dorsal epidermis of female genital segments. Males release spermatophores into the environment, and females pick them up with their ventral palps and first pair of parapodia. Stored sperm remain viable for fertilization for at least one month. Spermatophore release and egg laying are independent of the presence of the opposite sex. Advantages associated with this system are discussed, and include asynchronous reproduction, a long breeding season, reduced sperm loss, and reduced exposure to risks. This sperm transfer mode is the first reported in the family Onuphidae and is proposed for other small, tube-dwelling onuphids.

Lebensraum: paradoxically, population growth may eventually end wars

Population growth may progressively reduce 1 of the motives for making war. Namely, population growth threatens shortages of resources, and especially land. Impending shortages cause a search for ways to mitigate the shortages. The discoveries eventually produce greater availability of resources than if population growth and pressure on resources had never occurred. The argument runs as follows: 1) Rhetoric about resources scarcity induced by population density has often contributed to international conflict, even if economics has not been the main motive in making war. 2) In the pre-modern era, war to obtain land and other resources may sometimes have been an economically sound policy. 3) Politicians and others in industrially developed nations believe resources may still be a casus belli. 4) Land and other productive resources are no longer worth acquiring at the cost of war.

More on immigrants' earnings over time

Immigrants' earnings have been found to be below those of natives in the earliest years after immigration, but with time in the US, earnings catch up with and then surpass those of natives. The authors obtain this result using an alternate data set, confirming the previous work of Barry Chiswick. The catch up period is between 20 and 30 years, later than Chiswick's result. After adding variables for foreign education and English ability, the catch up period is only 3 years after entry. In a context where other variables are not held constant, the authors consider effects of discrimination in admission by schooling and age. Both are found to be powerful selection factors in increasing the earnings levels of immigrants.

On the optimum theoretical rate of population growth

"The paper seeks intuitively-satisfying models of optimum population growth. The authors build upon Phelps's model of endogenous technical progress plus the Steinmann-Simon extension, which imply that the per-person consumption growth rate depends positively and linearly upon the population growth rate, without bound.... They suggest that the consumption rate ultimately turns downwards as population growth increases because of decreasing adoption of available technology as labor cheapens relative to capital, and as high population growth overtaxes people's will and ability to respond. Including a convex-downward function in the model yields sensible results." (summary in GER)

The effect of immigrants on natives' incomes through the use of capital

"This paper deals with questions about the effects of immigrants on three types of capital: the private capital immigrants work with, the public (government) capital that immigrant workers use, and the public capital used for services by immigrants." The geographic focus is on the United States. The authors conclude that although the average cost to natives in 1975 dollars to provide services for immigrants is 4,172 dollars, this amount "is considerably smaller than the benefits of immigrants to natives through their relatively low use of welfare services and their relatively high contribution of taxes." Comments by Jacob Mincer (pp. 95-7) are included.

There is no low-level fertility and development trap

Summary The theory of the low-level equilibrium trap asserts that an increase in income stimulates population growth sufficiently so that the additional people 'eat up' the 'surplus' over subsistence, and hence drive the level of income back to subsistence. Originally the theory referred primarily to mortality, but nowadays its application is to fertility. In the long-run equilibrium context in which the theory is ordinarily presented, the fact that the long-run elasticity of fertility with respect to income is negative in less developed countries fatally contradicts the accepted version of the trap. But to give every chance for trap theory to be meaningful, the paper presents a period-by-period analysis, embodying larger-than-observed positive elasticities during the early years and the logically necessary counterbalancing negative elasticities during the later years. These elasticities are combined with consumption and production figures for various age groups to estimate the effect in each year after the windfall, and altogether. The results show that even under assumptions not charitable to the conclusion of this paper, additional children do not even come close to 'eating up' the increase in income which induced their births, so that the trap theory is falsified.

Resources, population, environment: an oversupply of false bad news

False bad news about population growth, natural resources, and the environment is published widely in the face of contradictory evidence. For example, the world supply of arable land has actually been increasing, the scarcity of natural resources including food and energy has been decreasing, and basic measures of U.S. environmental quality show positive trends. The aggregate data show no long-run negative effect of population growth upon the standard of living. Models that embody forces omitted in the past, especially the influence of population size upon productivity increase, suggest a long-run positive effect of additional people.

Puzzles and further explorations in the interrelationships of successive births with husband's income, spouses' education and race

When fertility is examined in the detail of individual parity progressions and birth-order transitions, important interactions between the effects of income and education are seen. Among the findings are: the negative effect of education on fertility is stronger at all parities for less educated compared to more highly educated women. Additional income has a more positive effect for more highly educated than for less educated women. For women with 0-8 years of education the effect of more income is positive when the family has no children but negative thereafter, but for college-educated women the effect of more income is positive. And additional income has a less positive (more negative) effect on fertility among nonwhites than among whites.

The welfare effect of an additional child cannot be stated simply and unequivocally

There is no single calculable welfare effect of an additional person. Rather, there are many different judgments, which may be negative or positive. The welfare effect depends upon the particular economic situation the child will be born into, which point in his life-cycle one refers to, whether he is expected to have a positive effect upon his particular sort of economy and society during and after his lifetime, and most of all, on the kind of welfare criterion used. Furthermore, no matter which welfare criterion is used, the welfare effect of an added individual summarized over time is especially sensitive to the particular assumptions made.

Multiple cerebral abscesses complicating hepatopulmonary amebiasis

A 3-year-old boy with hepatopulmonary amebiasis treated with chloroquine phosphate for 20 days subsequently was found to have three brain abscesses and responded to prolonged combined therapy with metronidazole and chloroquine phosphate. Cerebral amebiasis should be considered in any patient with amebic dysentery, hepatic abscess, or pulmonary involvement in whom signs or symptoms of central nervous system involvement appear. A prolonged course of appropriate therapy with periodic brain scanning for evidence of improvement is suggested.