ANIMAL PRODUCTION. 171 



The problem of age, growth, and death, C. S. Minot (New YorJc and London, 

 li)08, pp. XXII +230, figs. 73). — This book summarizes the results of investi- 

 gations on the correlation of age and growth and attempts to throw light on 

 the problems of growth, differentiation, senescence, and death by the demon- 

 stration of laws governing the proportionate volume of the nucleus and cell 

 body in the growing organism. It is based largely on investigations of the 

 author. 



Measurements of growth, or increase of protoplasm, show very rapid gains 

 for a short time in the early stages of an organism. A few days after birth a 

 chick may add 9 per cent of its weight in a single day, but the rate of growth 

 diminishes rapidly until at 2 months of nge it never adds more than 3 per cent 

 per diem to its weight and at 3 months only 1 per cent. A male rabbit the 

 fourth day after its birth may add over 17 per cent of its weight per diem, and 

 at 2i months only 1 per cent. Growth curves of chickens, guinea pigs, rabbits, 

 and human beings are given. The appendixes contain a description of an 

 age-reckoner, data on the growth of rabbits dud cliickens. and related matters. 



The author sums up his investigations by formulating 4 laws: "First, reju- 

 venation depends on the increase of the nuclei. Second, senescence depends 

 on the increase of the protophism, and on the differentiation of the cells. 

 Third, the rate of growth depends on the degree of senescence. Fourth, senes- 

 cence is at its maximum in the very young stages, and the rate of senescence 

 diminishes with age. As the corollary from these, we have this — natural death 

 is the consequence of cellular differentiation. . . . 



" If it be true that the growing old depends upon the increase of the proto- 

 plasm, and the proportional diminution of the nucleus, we can perhaps in the 

 future find some means by which the activity of the nuclei can be increased 

 and the younger system of organization thereby prolonged." 



The "presence and absence" hypothesis, G. H. Shull (Amer. Nat., JfS (1909), 

 \o. 511, pj). JflO-JiW). — The aim of the author is to show that the dominance 

 of " absence " over " presence " can be explained without recourse to inhibiting 

 factors. Simple chemical experiments are cited to show that what appears to 

 be a pair of characters is really the presence and absence of a single character. 

 When absence dominates over presence the positive character is latent in the 

 heterozygote. Visible Mendelian characters are always secondary and are 

 dependent at some stage of analysis upon chemical reaction. 



Inheritance of yellow color in rodents, A. L. Hagedoorn {Univ. Cal. Pitbs., 

 Phijs., 3 (1909), Xo. 14, pp. 95-99). — This is a discussion of results obtained 

 by recent experiments on the subject. 



The author thinks it probable that Castle's barring factor is in reality com- 

 posed of 2 factors, one of which is the modifying factor present in the domi- 

 nant strains of yellow rodents. Its action is seen in a partial inhibiting of the 

 2 darker pigments whenever these are present with it in one zygote, for which 

 is proposed the name " inhibiting factor." The barring of the hairs and the 

 body markings should then be due to the other component of Castle's barring 

 factor, for which is proposed the name " marking factor." 



The other conclusions reached are as follows: "Different strains of yellow 

 rodents exist, the differences between the strains being due not only to pig- 

 ments but also to other definite modifying factors. Yellow mice are not neces- 

 sarily heterozygous. A reversion of the order of dominance does not. take 

 place. It is impossible for one pigment to dominate over another. The pres- 

 ence of one pigment is simply dominant over its absence. Bateson's hypothesis, 



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