Ill INDUCTION GENERAL REMARKS 479 



could be established. "Organizin" now appears as a convenient general designation 

 for the variety of ribonucleoproteins, which are the main agents of induction. 

 This situation still conforms to the general idea we had in mind when we coined 

 the term. 



(/) On the intimate changes in the reactor 



Induction, like hormonal excitation, is primarily a trophic process. Cells with a 

 limited range of activity receive a stimulus which suddenly raises their metab- 

 olism to an unforeseen level and causes differentiations of definite structural and 

 functional character. The prinmm movens in these changes remains unknown. If we 

 can accept the suggestion that a ribonucleoprotein is introduced, it is probably 

 attacked first by a proteinase, then by the cell ribonuclease, and the various frag- 

 ments of the molecule introduced into chains of unknown but imaginable reactions. 

 It is known that one of the earliest consequences is a considerable increase of the 

 RNA-rich granules, and that this change persists in the daughter cells. Simul- 

 taneously, the alkaline phosphatase synthesis takes place. These changes are so 

 intense and so stable that they suggest, as I already mentioned above, what I have 

 called (1940) a metabolic contagion. This expression, although vague, at least em- 

 phasizes the rapid repetition of some reactions, perhaps the multiplication of 

 discrete particles, which may, or may not be similar to plasmogenes. In such a 

 scheme, the first step would be accomplished by a proteolytic enzyme, which 

 conforms to the hypothesis formulated by Lallier (1955) on the basis of indirect 

 but convincing arguments. A permanent treatment of newt eggs by zinc acetate, 

 from cleavage on, causes thickenings and expansions of the neurula epiblast, 

 especially in the fields of active induction. The abnormality may be considered 

 as a resvdt of an effect upon the competence of the reacting epiblast. On the other 

 hand, formaline which combines with amine groups and reduces the activity of 

 proteolytic enzymes, is known to suppress induction. The author suspects that 

 the link between this blockage, the Zn effects, and the autonomous neuralization 

 of ectoblast in abnormal conditions concerns proteolytic enzymes. In my opinion, 

 this interesting hypothesis should be applied to the events occurring inside the 

 reactor more than to the activity of the inductor itself. 



For a deeper comprehension of these changes, the most important fact that 

 certain inimical conditions are sufficient to cause autonomous, brain-like neurali- 

 zation cannot be neglected, and is not antinomic with the last remarks. 



IV. FINAL CONSIDERATIONS 



This survey has brought the analysis to the stage when conditions are prepared 

 for further differentiation of the embryonic rudiments and for the growth of 

 tissues and organs. Beginning with the formation of gonocytes, it has led us to 

 an organism possessing young gonads, so that the reproductive cycle is virtually 

 complete. 



During the days or weeks when a new organism is being created, no stage is 

 insignificant and no part of the system can be lost of view without inconvenience. 



Literature p. 483 



