436 



GERMINAL ORGANIZATION 



INDUCTION PHENOMENA 



notogenic action of the tissue used, although the richness in ribonucleoproteins 

 is much reduced in the 3d specimen; also, specimens 4 and 5, 7 and 9 reveal 

 opposite actions in spite of their approximately equal RNA content. This, how- 

 ever, does not exclude a role of the ribonucleoproteins which could be based, as 

 we shall soon learn, on more specific properties. Thirdly, the concept of the main 

 acting inductors — whether two or three in number — is much clarified. It may 

 be added to the characteristics mentioned on p. 432 that extraction with con- 

 centrated NaCl (specimens 6, 7, 8) favors acrogenesis. Since the frequency of 

 inductions remains approximately constant, it is unlikely, as the authors rightly 

 say, that we have to do with a selection of preformed substances. A transformation 

 of the primary notogenic inductor (and of its deutogenic part, if it is worth being 

 distinguished) into the acrogenic one appears nearly certain. These remarks lead 

 the authors to the interesting opinion that the available data do not exclude the 

 fundamental singleness of the inductive agent: 



Fig. 87. Remarkable xeno-induction by a proteinic extract. Elongation of the explant and 



induction of a spinal cord and ectomesoblast without presence of chordomesoblast. 



See text. From Yamada and Takata, 1955. 



"A protein or protein complex present in the tissue in its native, unstable state induces 

 spino-caudal structures; this state is easily and irreversibly transformed into a stable one 

 in which the same protein or its complex induces archencephalic structures. During the 

 transitional phase of this transformation the same protein gives rise to deuterencephalic 

 induction", and further . . . "the so-called spinocaudal, deuterencephalic and archen- 

 cephalic factors of the tissue all would belong to one chemical category or to a group of 

 closely related proteins and form one series of structural transformations, which can be 

 released easily by different treatments". 



This statement is in close agreement with some of our preceding remarks 

 (p. 401, 410) and will be an essential argument in our general interpretation. 

 The last step will be devoted to a reconsideration of the role of ribonucleoprotein 

 complexes. After his discovery of the so strongly suggestive relation between RNA 

 and induction (p. 360), Brachet looked for experimental evidence in favor of this 

 relation. He found (1944, p. 418) that the higher the RNA content of a xeno- 

 inductor, the higher was the percentage of positive results. The most efficient 



