Multitrait estimation of genetic parameters of lactation curves in Holstein heifers

Weekly milk yields of 1022 Holstein heifers from 61 sires were used to derive coefficients of the lactation curves using modified gamma and inverse polynomial functions. The natural logarithm of a modified gamma function was ln(yn) = ln (a) + b ln (n) + cn + u sin (x) + v cos (x), where a, b, c, u, and v are coefficients to be estimated; n is the day of lactation; and x is the day of year. Estimates of a, b, and c were combined to define persistency [-(b + 1) ln c], week of peak yield (b/c), and peak yield [a(b/c)be-b]. The inverse polynomial function was n/yn = A0 + A1n + A2n2, where A0, A1, and A2 are coefficients to be estimated. Variance and covariance components for the coefficients of the lactation curve were estimated by the multitrait restricted maximum likelihood method using canonical transformation. Heritability estimates were ln (a) .11, b .07, c .04 u .01, v .04, A0 .28, A1 .26, A2 .21, persistency .21, week of peak .18, peak yield .23, and 308-d milk yield .41. Genetic correlations indicated that selection for faster rate of increase to peak production would result in higher 308-d milk production, higher peak yield, and greater persistency.

Cementing technique and the effects of bleeding

We report the results of simple laboratory experiments which showed that bleeding pressures known to occur at the bone surface during total hip arthroplasty may compromise the integrity of the bone-cement interface and the cement itself. Such undesirable effects can be prevented by maintaining adequate pressure on the cement until its increased viscosity can resist displacement caused by the bleeding pressure.

Expression of c-myc during differentiation of the human teratocarcinoma cell line Tera-2

The quantity of c-myc mRNA was measured during the retinoic-acid-induced differentiation of the pluripotent human teratoma cell line, Tera-2 cl. 13. As the cells were exposed to retinoic acid for longer periods of time the duration of the cell cycle progressively increased (measured by the rate of S phase entry) until the cells were effectively quiescent and expressed characteristic differentiation markers. Under these circumstances steady-state levels of c-myc expression increased by up to 1.6-fold with respect to rapidly growing undifferentiated cells. Southern blot analysis of the c-myc genes in Tera-2 indicated no major rearrangement or amplification in the cell line.

Real-time deformation invariant optical pattern recognition using coordinate transformations

The well-known scale and rotation invariant polar-logarithmic coordinate transformation is used to achieve in-plane distortion invariant pattern recognition. The coordinate transform is produced by a computergenerated hologram on a laser printer. Attention is given to weighting terms in the output and their effect on resolution and the number of input plane pixels removed near the origin. The optically produced coordinate transformed input pattern is interfaced to a correlator by a pocket liquid crystal TV to provide real-time processing. Experimental results are included.

Computer generated hologram recording using a laser printer

The use of a laser printer for recording various types of computer generated holograms is discussed, and initial results are presented.

Association of milk protein types with growth and reproductive performance of dairy heifers

A total of 890 heifers was used to study the effects of four milk protein loci (alpha S1-casein, beta-casein, kappa-casein, and beta-lactoglobulin) on heifer growth and reproduction. The additive effects of gene substitutions at the four milk protein loci were significant only in 4 of 56 cases for all traits studied. Dominance effects at alpha S1-casein, beta-casein, and kappa-casein loci were not significant for any traits except beta-casein locus on body weight at first calving. Heifers with AB type of beta-lactoglobulin showed greater body weights and measurements and gestation length than the AA or BB type, indicating an overdominance effect. Heifers with AB type of beta-lactoglobulin were significantly younger at first conception and at first freshening and had fewer number of days from first service to conception than the AA or BB type, indicating underdominance effect. Thus, beta-lactoglobulin locus shows overdominance, underdominance, or no dominance, depending upon the traits considered. The four milk protein loci contributed more dominance variance than additive variance to total phenotypic variance. This might account for the existence of milk protein polymorphism in the cattle population. The combined genotypes of the four milk protein loci showed significant effects on 2 of 14 traits studied.

Molecular cloning of cDNA for human prostatic acid phosphatase

A human liver cDNA library in lambda gt11 was screened with polyclonal antiserum to human acid phosphatase isoenzyme 2a/4. About eleven positive clones have been obtained. Two clones, lambda Hap21 and lambda Hap22 were further characterized: clone lambda Hap21 contained a 0.8-kb cDNA insert and clone lambda Hap22 a 1.8-2.0-kb insert. XbaI digestion of lambda Hap22 generated two fragments of 1.0 and 0.9 kb. BglII digestion resulted in a 1.2-kb fragment and several smaller fragments of undetermined size. Clone lambda Hap22 contained all the genes carried by lambda gt11(lac5cI857nin5Sam100) and the 2-kb insert. An Escherichia coli(lambda Hap22) lysogen was generated, and its acid phosphatase activity was approximately ten-fold higher than that in the control nonlysogenic lysate. Western-blot analysis of total proteins present in this E. coli(lambda Hap22) lysate revealed that the non-induced lambda Hap22 prophage directed the synthesis of an approx. 175-kDa protein. This protein was recognized by antibody to the human acid phosphatase isoenzyme 2a/4 and anti-beta-galactosidase and was produced only upon induction with IPTG. These results indicated that lambda Hap22 carried a major portion of the gene coding for the human acid phosphatase isoenzyme 2a and/or 4 and this protein fragment of acid phosphatase was sufficient to manifest enzymatic activity.

Role of the collar on the femoral stem of cemented total hip replacements

Three dimensional finite element models with realistic loading conditions were used to analyse the role of the collar of cemented total hip stems. Three types of implant were considered: large collared stems, small collared stems and totally collarless stems. A computer model of the natural femur provided an indication of the bone stresses before hip replacement, and thus aided the identification of possible mechanisms of bone resorption. In particular, resorption of the medial femoral neck was examined, and its effect on the stress distribution within the stem-cement-bone structure is discussed. The results indicate that loss of bone at the femoral neck is a serious symptom for any design of implant. The factors leading to the resorption are complex but it is clear that it is not a consequence of simple stress shielding of the bone. The most likely cause is the manner in which the stem moves within the femoral shaft, which is a function of whether the stem is collared or not.

Sequential estimation of genetic and phenotypic parameters in multitrait mixed model analysis

Single-trait and multitrait (2-, 3-, 4-, and 5-trait) restricted maximum likelihood methods were applied to the same set of data with complete information on all traits. Results suggest that parameter estimates from a data set vary depending upon the type of analysis (single- or multitrait model) and upon the other traits included in multitrait analysis. The choice of parameter estimation method for a breeding design should be based on the breeding goal. In parameter estimation or sire evaluation, traits included in a multitrait analysis should correspond to the traits of interest in the breeding goal. Multitrait analysis explores all intercorrelations simultaneously in parameter estimation and thus provides a complete picture of all interrelationships among traits. In contrast, single-trait analysis produces pairwise (simple) correlations and ignores the possible contribution of other related traits under study to the pairwise correlation. The 5-trait model analysis through canonical transformation was about 300% more efficient in terms of computer time than single-trait model analysis of the same 5 traits. In this study, parameter estimates converged faster under multitrait analysis through canonical transformation than under single-trait analysis.

Production and reproduction of early and late bred dairy heifers

A total of 253 heifers bred at first estrus after 350 d of age (350-d breeding age group) and 249 contemporary heifers bred at first estrus after 462 d of age (462-d breeding age group) were used to study the effects of age at first breeding on productive and reproductive performances of first lactation heifers. Heifers of both breeding age groups were subject to similar feeding and management practices. The average age at first calving was 698 d for the 350-d breeding group and 796 d for the 462-d breeding group. Although not statistically significant, heifers of the 462-d breeding group tended to have a higher conception rate at first service (47 vs. 38%) and fewer days between first service and conception (39 vs. 44 d) than those of the 350-d breeding age group. Breeding heifers as early as 350 d of age has no adverse effects on calving ease or retained placenta but does result in calves 1.2 kg lighter at birth. Heifers of the 350-d breeding group had lower milk, protein, and fat yields at both 168 and 308 d of first lactation than those of the 462-d breeding group. A 1-d reduction in age at first calving decreased 308-d milk yield by 2.01 kg for the 350-d breeding group as compared with 4.74 kg for the 462-d breeding group.

Multitrait estimation of relationships of first-lactation yields to body weight changes in Holstein heifers

An experimental population of 994 Holstein heifers from 56 sires was used to estimate simultaneously heritabilities and genetic and phenotypic correlations between first-lactation yields and prepartum and postpartum weight changes. Variance and covariance components were estimated by the multitrait restricted maximum likelihood method. Heritability estimates were .09, .15, and .32 for first-lactation milk, protein, and fat yields. Heritability estimates ranged from .20 to .34 for prepartum and postpartum body weights and weight changes of first lactation. Weight gain from 350 to 462 d of age was highly correlated, genetically and phenotypically, with first-lactation milk, protein, and fat yields. Genetic and phenotypic correlations between first-lactation yields and body weights at calving and at 56, 112, 168, 224, and 280 d postpartum were positive, suggesting that the larger heifers had higher lactation yields. In contrast, genetic and phenotypic correlations between yields and weight gains during the first lactation were negative, indicating that high-producing heifers gained less weight during lactation than low-producing heifers. Heifers lost an average of 23 kg from calving to 56 d postpartum and gained weight thereafter. On genetic and phenotypic scales, larger heifers at first calving lost more weight from calving to 56 d postpartum and gained less weight from 56 d postpartum onward than smaller heifers.

Sire and sire-feeding regimen interaction effects on lactation, growth, and carcass traits in dairy cattle

Data from the University of Illinois dairy herd were used to estimate heritabilities of lactation yield, growth rate, and carcass traits and genetic correlations among them and to evaluate the importance of sire and of interaction of sire with feeding regimen for these traits. Heritabilities for lactation, growth, and carcass traits were small or moderate. Genetic correlations of lactation with carcass traits were moderate negative or large positive. Genetic correlations of estimated average daily gain with lactation and carcass traits could not be estimated. Variance for interaction of sire with feeding was large relative to sire variance for estimated average daily gain. Similarly, variance for interaction of sire with feeding regimen was large for back fat thickness, chilled carcass weight, dressing percentage, maturity score, and yield grade. Interaction of sire with feeding should be considered in genetic studies or in sire evaluation for some carcass traits and average daily gain.

Effects of rate review on the financial viability of New York hospitals: a retrospective assessment

This article reports the findings of a study analyzing the effects of rate setting on the financial condition of New York hospitals from 1974 to 1980. During this period, the New York rate review system was considered one of the most stringent--and successful--cost containment programs in the county. The conclusions of this study indicate that there may be serious long-term consequences of cost containment programs of this type.

Reproductive performance of crossline and pureline dairy heifers

Data of 2779 purebred and crossbred heifers collected from five research stations of Agriculture Canada were used to study additive and nonadditive genetic effects on ages at first heat and at first breeding and conception rate at first service. Of these heifers, 2378 heifers had information on ages at first conception and at first freshening, days from first service to conception, and gestation length. The model included station, year of birth, sire, breed additive, maternal, and heterosis effects where sire effects were treated as random. Station differences were a significant source of variation for all reproductive traits. Year of birth had significant effects on four of seven reproductive traits. Breed additive effects for all genetic groups were not significant except for Finnish Ayrshire and American Holstein. No significant maternal effects were detected. Of 21 combinations of heterosis effects, six combinations showed significance. Partial regression coefficients ranged from negative to positive, suggesting that breed additive, maternal, and heterosis effects could increase or decrease for each percent increase of genetic contribution, depending upon the trait, breed group, and type of inheritance.

The Bedford-Stuyvesant/Crown Heights demonstration project

The Bedford-Stuyvesant/Crown Heights demonstration project in Brooklyn, New York, provided Federal and New York State funds to offset the deficits of three hospitals and three freestanding health centers while the six institutions worked to improve service quality and financial viability of the local health care system. The demonstration project resulted in a merger between two of the participants: at the end of 1982, the Jewish Hospital and Medical Center of Brooklyn and St. John's Episcopal Hospital of Brooklyn merged to form Interfaith Medical Center.

Evaluation of cow reproduction in the pureline foundation phase of the Canadian National Dairy Cattle Breeding Project

Five reproduction traits--number of inseminations per cow, days to first estrus, days open, calving interval, and culling rate for infertility--were studied on dairy cows from a long-term breeding project of the Agriculture Canada Research Branch. Five experimental farms maintained either Holstein line, Ayrshire line, or both. Traits were analyzed within each line by a model in which station, year, sire group (paternal parentage), and bull (cow's mate) were considered. Variation these factors caused was small; most represented less than 1% of the total sum of squares. Holstein cows at Lethbridge, Lennoxville, and Ottawa had 1.9, 2.3, and 2.0 inseminations per cow, 55.1, 63.9, and 51.2 days to first estrus, and 109.9, 125.2, and 112.4 days open. The same traits of Ayrshire cows at Charlottetown, Normandin, and Ottawa were 2.3, 2.2, and 2.0; 53.3, 61.4, and 53.0 days; and 105.2, 129.2, and 114.5 days. All three traits were derived from records of all cows, including those that did not complete calving intervals. Calving interval at all five stations varied from 376.1 to 412.4 days. Intensity of culling for infertility differed between stations, e.g., 5% in one and 31% in another. About 24% of all disposed cows were culled in both lines for infertility.

How nursing homes behave: a multi-equation model of nursing home behavior

This paper estimates a multi-equation model of nursing home behavior using the 1973 NCHS National Nursing Home Survey for data. The paper investigates empirically the effects of public reimbursement and regulatory policies, as well as other exogenous factors, on the following dependent variables: (1) average operating cost; (2) nursing hours per patient-day; (3) an index of rehabilitation-type services; (4) the occupancy rate; (5) the mix of public and private patients; and (6) the rate charged to private patients. The results dramatize the importance of endogeneity concerns in nursing home behavior. Rate setting and many regulations are shown empirically to have unintended and often undesired consequences on cost and other policy criteria of interest. While there has been anecdotal evidence of such system-wide interdependencies, this study affirms that such possibilities must be taken seriously. Rational nursing home regulation cannot proceed apart from a comprehensive understanding of the nursing home behavioral environment.

Evaluation of the maximum allowable cost program

This article summarizes an evaluation of the Maximum Allowable Cost (MAC)-Estimated Acquisition Cost (EAC) program, the Federal Government's cost-containment program for prescription drugs. The MAC-EAC regulations which became effective on August 26, 1976, have four major components: (1) Maximum Allowable Cost reimbursement limits for selected multisource or generically available drugs; (2) Estimated Acquisition Cost reimbursement limits for all drugs; (3) "usual and customary" reimbursement limits for all drugs; and (4) a directive that professional fee studies be performed by each State. The study examines the benefits and costs of the MAC reimbursement limits for 15 dosage forms of five multisource drugs and EAC reimbursement limits for all drugs for five selected States as of 1979.

The determinants of nursing home operating costs in New York State

This paper investigates the determinants of nursing home operating costs in the State of New York during 1975. The analysis indicates that "scale" and occupancy are minimally important in determining operating cost variation. In contrast with other studies, patient- and service-mix differences are found to be important, although reimbursement grouping variables (e.g., profit/nonprofit) remain the most significant and important variables. Having estimated one of the most general cost functions to date, the authors ask what accounts for these differences if not differences in the patient mix, service mix, or input prices. If the differences are merely due to unmeasured differences in the amenity level of care or to managerial inefficiency, then it is not clear that public programs should continue to discriminate between facilities in these categories and pay the differences.

Interactions of sires with feeding and management factors in Illinois Holstein cows

Components of phenotypic variation in milk yield from interactions between sires and several feeding and management factors were estimated. Milk yield data were first lactation records. Feeding and management data from Illinois Holstein Dairy Herd Improvement herds were obtained by questionnaires. Sire-herd interaction component was 10% of phenotypic variance in milk yield. Components of variance from interaction between sires and three feeding and management factors, namely, source of roughage for milking herd during summer, amount of grain fed to heifers between 12 and 18 mo age, and amount of grain fed to heifers during 2 mo before calving were negative. Interaction between sires and ideal weight for breeding heifers accounted for 3% of phenotypic variation in milk yield.

Why do nursing home costs vary? The determinants of nursing home costs

Since the costs of nursing home care are a major component of the rapidly rising costs of health care, it is appropriate to base public policy discussions about cost containment on the determinants of nursing home costs. This article investigates the determinants of nursing home operating costs and reviews the results of 11 related econometric cost analyses conducted by the authors. Single-equation cost analyses are developed for nursing homes in three states and in the nation. The cost results of a multi-equation model of nursing home behavior are also reviewed. The analyses indicate that facility size and occupancy rate are minimally important in determining cost variation. Facility characteristics, particularly type of facility and ownership, are important variables. Nonprofit facilities consistently had higher costs than for-profit facilities, after controlling for patient mix and service differences, and, in one analysis, for a measure of quality.

The prevention of post-appendicectomy sepsis by metronidazole and cefazolin: a controlled double blind trial

A double blind, randomized, controlled trial was carried out at two hospitals to try the effect of metronidazole, which is effective against most anaerobes, and cefazolin, which is effective against many aerobic organisms, singly and in combination, on the incidence of wound sepsis following appendicectomy. Patients were placed at random into one of four groups; to receive metronidazole and placebo, cefazolin and placebo, metronidazole and cefazolin, or double placebo. Patients with generalized peritonitis were excluded for ethical reasons. Treatment was started before operation and continued eight-hourly for twenty-four hours. All patients in the trial were followed up at about two weeks after discharge from hospital and their wounds inspected. Two hundred and seventy-one patients were assessed. Sepsis rates at the two hospitals were similar. On the untreated controls, 30% discharged pus from their wounds, and in the groups receiving one drug only, about 20%. In those receiving both drugs the infection rate was 3%, a highly significant difference from that in the other three groups.

Comparison of three methods of immunization against bovine anaplasmosis: an examination of postvaccinal effects

Normandy calves ranging in age from 7 to 11 months were immunized against bovine anaplasmosis, using a diluted virulent Anaplasma marginale stabilate of Colombian origin, diluted bovine blood containing an apparently mild strain of A marginale isolated in Colombia, or an attenuated A marginale vaccine of ovine origin from the United States. Calves given the stabilate generally showed a moderate degree of parasitemia and reduction in packed cell volume (PCV). Calves given the apparently mild Colombian isolate of A marginale developed a moderate parasitemia, a reduction in PCV, and in some instances, required treatment to moderate the premunization procedure. Calves given the attenuated vaccine showed minimal evidence of parasitemia and PCV reduction. Most of the immunized calves became seropositive in the complement-fixation test for anaplasmosis and all calves sampled showed evidence of a cell-mediated response, using the leukocyte migration-inhibition test.

Comparison of three methods of immunization against bovine anaplasmosis: evaluation of protection afforded against field challenge exposure

The efficacy of three immunization methods for bovine anaplasmosis was tested on 88 yearling Normandy cattle which were challenge-exposed under field conditions in an enzootic zone in Colombia, South American. A total of 30 cattle were immunized (premunized) with a presumed mild Colombian isolate of Anaplasma marginale; 29 calves were vaccinated with an attenuated A marginale of ovine origin; and 29 were exposed to a virulent A marginale stabilate of Colombian origin. Twenty-nine nonvaccinated cattle served as controls. Parasitemia, packed cell volume, body weight, and complement-fixation antibody response were monitored to determine host response to challenge exposure. The calves experienced a Babesia challenge exposure following arrival in the enzootic zone, after which a transient increase in Anaplasma parasitemia, accompanied by a decrease in packed cell volume, occurred in most of the vaccinated calves. However, neither clinical anaplasmosis nor mortality due to the disease occurred in the immunized cattle. Twenty-seven of the nonvaccinated calves had signs of clinical anaplasmosis and five (17%) died of the disease.

Blood metabolic profiles: their use and relation to nutritional status of dairy cows

Profiles of blood metabolites have been used widely to identify problem herds and to indicate dietary causes of disease or low production. Related herd survey studies and designed experiments are reviewed. An initial study of profiles and estimated nutrient intake of five "normal" and four "problem" herds was conducted between 1972 and 1974 to establish baseline values for blood metabolites. Profiles of blood metabolites for additional problem herds were obtained during 1974 through 1977. Variation due to herd of origin, production, stage of lactation, and season of year are important causes of variation in concentrations of metabolites in jugular blood of dairy cows. They need to be considered carefully in interpreting profiles of blood metabolites. Several relationships between dietary intake of nutrients and concentrations of associated components in jugular blood are significant. Concentrations of metabolites are of almost no practical use for individual cows because of extreme variations in diet required to generate abnormal concentrations of blood metabolites. Averages of glucose of blood and nitrogen in urea on seven to ten cows, adjusted for the factors mentioned above, have limited practical value in detecting inadequate energy and protein intake, respectively.

Some clinically relevant variables affecting the mechanical behaviour of bone cement

The effects of 12 clinically relevant variables upon the basic mechanical properties of acrylic cement are reported. Attention is drawn to the facts that these variables may at times coexist to lead to serious reductions in the strength of the cement, and that the operating surgeon may exercise a substantial influence on the effective mechanical properties of the cement he is using.

The shear strength of trabecular bone from the femur, and some factors affecting the shear strength of the cement-bone interface

The shear strength of trabecular bone from the femur has been studied. In general, the strongest trabecular bone is found close to the cortico-cancellous junction, though its shear strength depends also on the relationship of the trabeculae to the plane of shear. Some factors affecting the shear strength of the cement-bone interface have been investigated. In vitro, maximal cement-bone interface shear strength is obtained by exposing and thoroughly cleaning strong trabecular bone, and then forcing onto it under pressure low viscosity cement.

Efficacy of attenuated Anaplasma marginale vaccine under laboratory and field conditions in Colombia

Four-month-old Holstein-Friesian calves were inoculated with 3 different doses (1, 2, and 3 ml) of attenuated Anaplasma marginale vaccine. Vaccinated calves showed mild anaplasma parasitemia, slight decrease in packed cell volume, low serologic conversion, and no clinical illness. An artificial challenge exposure of vaccinated and unvaccinated calves with virulent Colombian A marginale showed that the vaccine provided protection against clinical signs of the disease, including parasitemia and anemia. The volume of the vaccinal dose did not alter the degree of protection provided. A 2nd group of 8- to 9-month-old Holstein-Friesian calves was then inoculated with 3 ml of anaplasma vaccine and premunized with both Babesia bigemina and Babesia argentina while being housed in an area free of these diseases. Calves were moved to an enzootic region heavily infested with various arthropods, including ticks, for natural field challenge exposure. Control calves, which were not given anaplasma vaccine, suffered clinical illness manifested by severe anemia and an average weight loss of 50.6 kg due to anaplasma field challenge exposure. In contrast, vaccinated calves did not show anemia and their weight loss was 3.9 kg.

The mechanical properties of bone cements

The mechanical properties of a number of commercially available bone cements have been investigated. Tests were carried out on specimens in compression, in bending and in tension. Using the compression test as a standard, the effects of the following variables were studied: the addition of antibiotics, strain rate, environmental temperature, and age. It was concluded that age, temperature and rate of straining have a marked effect on the strength of the cement, while the addition of small quantities of antibiotics only marginally weakens the cement.

In vitro aging of frozen bull semen

The change in fertility of bull semen with time in storage at -196 C was examined in data on inseminations by the Michigan Animal Breeders Cooperative over 5 yr. Intervals from collection to use were grouped by 10 days for the 1st yr, 30 days for the 2nd yr, 180 days for the 3rd yr, and a single class for semen stored 4 or 5 yr. There were 97,586 first inseminations from bulls with 10 or more ejaculates and from ejaculates with four or more classes. Nonreturn rates for 50-, 60-, 90-, and 180-day intervals post-breeding were calculated. Heterogeneity of quadratic regressions of nonreturn rates on semen age was unimportant. Both regression and least squares analyses were used. Nonreturn rates increased to about 115 days of storage and remained there through the 4 and 5 yr age group. The lowest and highest nonreturn rates for a return interval differed by approximately 4%. Maximum differences in nonreturn rates for different intervals were at the lowest nonreturn rates.

Selection effects on a linked neutral locus

Selection changes the frequency of alleles at a linked locus as well as at those under selection if the population is not in linkage equilibrium. The magnitude of this frequency change depends on the tightness of the linkage, the selection intensity, and the deviation from linkage equilibrium. Allowing a population to mate randomly without selection brings the population closer to linkage equilibrium. This decreases the effect of selection on allelic frequencies at a linked neutral locus. However, if linkage is very tight it can take many generations to make a large difference in the effect of the linked locus. The loss due to undesirable changes in allelic frequencies at linked loci when the population is not in linkage equilibrium must be weighed against the time and effort saved by beginning intense selection for the primary trait in an early generation. Effects of selection intensity, linkage intensity, and delayed selection on changes in allelic frequency at a neutral linked locus are demonstrated.

Thermal aspects of self-curing polymethylmethacrylate

Bone necrosis adjacent to self-curing polymethylmethacrylate is a matter of accepted fact. Among the possible causes are mechanical and vascular damage from the preparation of the bone cavity, chemical damage from the monomer and free radicals in the cement dough, and thermal damage from the heat of polymerisation, occurring in this order. Consideration of the tissue reaction to this material, theoretical calculation of the heat output from polymerising acrylic and interface temperature profiles, experimental observations of interface temperatures and maximal temperatures at polymerisation, together with clinical observations, all lead to the view that the bone necrosis is not a consequence of thermal damage, which is unlikely to be a cuase of failure of prosthetic fixation. Temperatures recorded from within polymerising acrylic masses are related primarily to the amount of monomer polymerising and are of no clinical significance in the fixation of prostheses. Interface temperatures are related primarily to the surface area of the interface and the thermal characteristics of the cooler material.