February 14, 1908] 



SCIENCE 



249 



metabolism occurring. Here is a field of 

 work the cultivation of which promises re- 

 sults of the greatest value, Avhile at the 

 samei time broadly applicable. Take, for 

 example, the processes of growth as studied 

 in the earlier stages of embryonic life up- 

 wards. What is the character of the 

 processes by which the young organism is 

 able to> carry forward its rapid develop- 

 ment? What the nature of the chemical 

 changes in the construction and destruc- 

 tion of tissues constantly taking place dur- 

 ing growth, where of necessity cell nucleo- 

 proteins are conspicuous elements? These 

 questions can not be definitely answered 

 at present, but some work carried on in 

 our laboratory^^ at New Haven has in- 

 dicated quite clearly the presence of cer- 

 tain specific enzymes early in embryonic 

 life, while others common to the same 

 organs in the full-grown animal are wholly 

 wanting. Thus, it has been found in 

 embryo pigs that the liver contains 

 adenase, but no guanase ; the latter enzyme, 

 however, is present in the viscera of the 

 embryo. Further, nuclease is present in 

 the liver of the embryo, indicating that in 

 the embryonic stage of this animal autolytic 

 changes can take place in the liver; i. e., a 

 liberation of aminopurines from the 

 nucleoproteins of the forming hepatic cells, 

 while any, adenine set free can be trans- 

 formed by the deamidizing enzyme adenase 

 into the oxypurine hypoxanthine. Like- 

 wise, any g-uanine liberated can by action 

 of the guanase contained in the embryo 

 viscera be transformed into xanthine. 

 Here, however, reactions of this sort ap- 

 parently stop in the embryo, at least of this 

 particular species. The xantho-oxidase 

 and the uricolytic enzyme are not present 

 in the embryo, though quite abundant 

 after bii'th. In other words, in the em- 



" " Chemical Studies on Growth," Mendel and 

 Mitchell, American Journal of Physiology, Vol. 

 XX., p. 115, 1907. 



bryonic, growing organism, oxidative and 

 katabolie enzymes which are obviously con- 

 cerned in the gradual destruction of the 

 purine part of the nucleic acid complex 

 are wholly wanting; while those enzymes 

 which have to do simply with transforma- 

 tion and alteration of the purines, thereby 

 leading perhaps to the construction of 

 added nuclein complexes, are conspicuous. 

 Here, we see chemical evidence clearly sub- 

 stantiating our conception of the character 

 of the transformations taking ■ place in 

 embryonic tissue; in the embryo, synthet- 

 ical, constructive processes must naturally 

 predominate, and the chemical mechanism 

 present at that stage of development is 

 designed solely to meet the requirements 

 of synthesis and broad constructive power. 

 Later on, however, when the embiyo passes 

 into an independent existence, those 

 enzymes which have to do with katabolism 

 gradually appear, and assume their func- 

 tion side by side with the enzymes pri- 

 marily concerned in construction. 



Problems of this character naturally 

 lead us on to a consideration of the. chem- 

 ical aspects of fertilization, cell division, 

 and the relative significance of the cyto- 

 plasm and karyoplasm of the egg and 

 sperm cells in heredity, etc. As is well 

 known, the head of the spermatozoon is 

 essentially a cell nucleus, and like other 

 nuclei is composed mainly of nucleopro- 

 teins ; viz., compounds of nucleic acid with 

 protein material of a more or less basic 

 character. The only substance to be noted 

 in addition is a small admixture of an 

 organic iron compound known as karyogen. 

 The nucleoproteins of the spermatozoon 

 nucleus difiler, however, from the cor- 

 responding substances present in the 

 somatic cell nuclei in that the protein part 

 of the molecule is made up mainly of some 

 peculiar form of protein such as prota- 

 mine, which Kossel has defined as the 

 simplest type of protein material known. 



