II KINETIC AND CAUSATIVE ASPECTS 349 



A chromatographic analysis has detected numerous nucleotides in the un- 

 fertilized eggs, and recourse to the incorporation of ^^P has shown that adenosine 

 monophosphate and adenosinetriphosphate are also present and active in these 

 cells (Finamore and Grouse, 1958). The effects of developmental inhibitors on 

 the phosphorus balance of gastrulae have been studied (Gregg and Kahlbrock, 

 1957); by measuring the respiration of homogenised hybrid embryos (Gregg and 

 Ray, 1957) it has appeared that no synthesis of new enzymes occurs, but that 

 the changes in the early stages mostly concern the accessibility to the existing 

 enzymes. 



In sea-urchin eggs probable predominance of glycolytic processes in the animal 

 half and of proteolytic ones in the vegetative (antipolar) half (Lindahl, 1936), 

 or at least, differences in the nature of the proteins have been found, as shown 

 by the recent studies of R. Lallier (1956a) concerning the action of zinc and 

 sulfonic stains (especially chloro-azol sky blue). 



For more elaborate information concerning germ proteins, immunological 

 methods have proved most useful. The gradual formation of new antigens which 

 are probably related to the synthesis of new proteins have been established in 

 amphibians (Flickinger and Nace, 1952; Clayton, 1953; Spar, 1953; Nace, 1956) 

 and birds (Ebert, 1954). In the chicken blastoderm thoroughly explored by Ebert, 

 serological tests for cardiac myosin have shown that it begins to be detectable 

 during the appearance of the primitive streak, when the antigen is quite widely 

 distributed; when the streak is established, the antigen is present in the whole 

 ectophyll, but not in the endophyll; at the head process stage, it becomes re- 

 stricted to the lateral cephalic territories shown in explantations by Rawles (1943) 

 to be cardiogenic^ ; at this stage, at least one of the antigens, corresponding to 

 cardiac actin, is present (see Chapter 5). This often-quoted result is indeed 

 reminiscent of the old views which admitted a progressive restriction (Driesch, 

 1896) or a segregation (F. R. Lillie, 1929) of potentialities. The possibility has 

 been repeatedly suggested that several or even most enzymes could be present 

 as seeds in the germ; this could also be true for macromolecules. The point is 

 indeed important. If such biochemical preformism must be admitted, it would 

 mean that the impression of novelty in each further step of development would 

 not hold at the molecular level. However, the case of cardiac proteins may well 

 be a unique one, in which an important synthesis at first takes place in an entire 

 layer, and only subsequently is utilized differently according to the region; this 

 would be only a form of epigenesis. Cytochemistry of the mammalian egg also 

 speaks strongly in favor of a biochemical epigenesis, as far as the microscopical 

 level is concerned (Mulnard, 1955). 



Results of considerable interest will probably come to light in the near future, 

 thanks to the serological method, a still recent but very efficient tool. As an 

 encouraging example, let us quote again (p. 320) the recent experiment^ which 

 consists of preparing very active rabbit antisera against the main parts of neurulae 



^ For the metabolic characteristics of these heart forming areas, see Duffey and Ebert 



(1957)- 

 ^ See note p. 320. 



IJlerature p. 483 



