Showing papers by "Morris W. Foster published in 1954"

A turbidimetric assay for tyrosinase activity in frozen sections of mouse skin.

Abstract: SummaryA new sensitive and objective method for the turbidimetric assay of tyrosinase activity in frozen skin sections is described. The procedure involves the dispersion of both melanin and skin and hair keratin, from previously incubated sections, in hot molar Na2S and KOH. Turbidimetric readings are then obtained on the absolute scale of the Klett-Summerson photoelectric colorimeter. This method is immediately useful for determining order of effect, and, if sufficiently improved, might also be useful for comparing amounts of naturally occurring pigment in different skin and hair samples.

Wright's studies of effects of maternal age on spotting and polydactyly in the guinea pig

Abstract: In mammals, where early development takes place in an environment of maternal tissues, changing physiological conditions of the mother constitute a changing environment which can affect the outcome of a developmental process in the offspring, within the range of variation permitted by the hereditary constitution. For example, the age of the mother has been shown by the detailed studies of Wright’s 2 . and Wright and Chase4 to be a major factor, if not the most important factor, common to littermates in producing nongenetic variability in two different cases of inherited characters: spotting of coat and polydactyly in the guinea pig. The piebald pattern of pigmented and nonpigmented areas of the skin and coat depends primarily on a recessive Mendelian factor, s, with many minor genetic factors, with additive effects occurring in different strains.’ Even in highly inbred strains, however, there is much variation in relative amounts of pigmented and nonpigmented areas. An intensive study of the correlations between percentage of white and environmental factors, such as season of birth, size of litter, and age of dam, revealed that the mother’s age was a major factor, in a group of factors common to littermates, in producing nongenetic variability. This effect of maternal age is readily seen in TABLE 1.‘ It is evident that, with increasing age of dam, there is an increasing percentage of white in the offspring. The possible effect of age of sire was ruled out by mating males and females of widely differing ages. In these matings, age of dam was the deciding factor. Now, since the major change in the trend towards more white occurs during the period when the dam has not yet completed her growth (neatly complete at 15 months), Wright’ concluded that the effect of age of dam on the piebald pattern “must thus be considered an immaturity rather than a senescence effect.” The atavistic occurrence of a little toe on the hind foot of guinea pigs results in four hind digits instead of the normal three. The hereditary basis of this character was investigated by crossing an inbred strain {Strain D), breeding true to perfect development of the little toe, with three strains breeding true to the three-toed condition (Strains 2, 13, 32) , as well as with another strain (35) which produced approximately 31 per cent four-toed offspring3 Depending on which strain was mated with D, the breeding results indicated strain differences varying from one to four Mendelian factors of comparable importance. It is of interest in this connection to note that crosses between D and 2 gave results in F1 , Ft , and backcross very similar to those expected if the three-toed condition were due to a single dominant Mendelian factor. Only when the supposed segregantswere subjected to further backcross tests did it become evident that this simple explanation could not account for the inheritance of polydactyly.