438 



GERMINAL ORGANIZATION 



INDUCTION PHENOMENA 



Further investigations soon ascertained the following two facts : (j) ribonuclease 

 (or deoxyribonuclease) digestion of xeno-inductors from vertebrates does not 

 suppress induction (Englander et aL, 1953 ; Okazaki and Osawa, 1954; Tiedemann, 

 1955, Hayashi, 1955); Englander even observes, in certain experiments, an 

 intensification of induction, with an increased acrencephalic tendency; Vahs 

 (1957a) confirms this point for mouse kidney treated with ethanol {Einsteck 

 methode) ; and (2) proteolytic enzymes {i.e. pepsin, trypsin, and chemotrypsin) 

 do attack the inducing agents (Toivonen and Kuusi, 1948; Tiedeman, 1955; 

 Yamada and Takata, 1955). The agreement in these results does not, however, 

 preclude the possible role of ribonucleoproteins : the protein part of these may be 



•i-^ 



^><n:.,v- 



Fig. 89. Typical induction of an acrencephalon by the PT inductor (see legend, Fig. 88). 

 Note the relation with the implant (grey mass) ; the presence of optic vesicles, lenses, fore- 

 brain, olfactory placodes, and the absence of mesenchyme. Compare with Figs. 80, p. 418, 

 and 82, p. 424. From Hayashi, 1956. 



important enough to be inactivated by proteolytic digestion, while ribonuclease 

 may liberate parts of the RNA nucleosides, which would not exclude recombi- 

 nations with the aid of the enzymes contained in the living reactor cells. Brachet 

 has indeed insisted on the observation that any implant is immediately submitted 

 to the activity of the host enzymes, with results which cannot yet be elucidated. 



These considerations are sufficient to appreciate the full meaning of the last 

 results to be quoted. 



Two of them are intimately correlated, for the fractions described have been 

 obtained by practically the same method: one series from guinea pig liver 



