Ill 



EXPERIMENTAL MODIFICATIONS 



417 



matter by what means, became inductors even if they did not possess that property 

 while Uving. This discovery suscitated a systematic enc^uiry of the change pro- 

 duced by cooHng or warming definite territories, especially those of the dorso- 

 marginal zone. Studies of this type have been done mostly on the neurula rather 

 than the gastrula. 



Holtfreter's fundamental work (1934b, c) showed that heating to 60° or 100° C, 

 in or out water, did not make any difference, nor did the exact origin of the 

 embryonic fragments which he inserted in the blastocoele. In 1943, Barth and 

 Graff used freeze-dried anterior and posterior parts of the neurula axis, which 

 they inserted into explants of ectoblast. They found that while no mesoblast 

 induction took place, neural tubes or masses appeared; in the delay of culture 

 used by them, they did not acquire a definite structure. 



0.5 mm 



Fig. 79. Induction produced on the ventral side of the host Triturus pyrrh. by a boiled piece 



of organizer, (a) A reduced diencephalon with two optic vesicles, (b) A larger diencephalon 



with cyclopic eye. e. -optic vesicle; e(l). -pigment layer of optic vesicle; e(r). -retinal part of 



optic vesicle; l.-lens; N. -cerebral tissue; Ph.- pharynx. From Okada and Hama, 1944. 



Okada and Hama (1944) fixed their attention on the uninvaginated part of the blastopore 

 lip, at the stage of the crescent shaped blastopore, and compared what it yielded and 

 induced {a) when affixed in the blastocoele, (b) when inserted in the same cavity after 

 previous boiling for 10 to 15 sec. (Fig. 79), (c) when explanted, in the living state, in 

 ectoblast. Their results are summarized in Table 4. 



Although the numbers are rather small, it is plain that the heat treatment has profoundly 

 modified the inducing capacity of the investigated material. Its ability to induce notogenetic 

 structures has completely disappeared; its ability for acrencephalic induction, only 

 exceptional in vivo, has become generalized. Explantation of the living material confirms 

 that its inducing ability takes in vitro a more acrencephalic character, but the change is 

 only of an intermediate nature. With the boiled inductor, the reaction often tends to 

 produce a minimum of brain tissue with an exaggerated optic vesicle (Fig. 79) ; the 

 absence of true telencephalon is suggested by the absence of olfactory placode (9 of the 

 II cases). This predominance of the optic vesicles recalls Gallera's observations (p. 371). 

 It also recalls an older result of Lopashov (1935) who obtained such an organo-specific 

 effect by using boiled optic vesicles as an inductor. Unfortunately, the Japanese authors 

 do not relate the localization of the reaction with the dead implant. Whatever may be 

 this relation, the difference in results after boiling can be explained in several ways, 

 ranging from differences of thermostability to the transformation of the notogenetic inductor 

 into an acrencephalic one. 



Literature p. 48-) 



