£11 EXPERIMENTAL MODIFICATIONS 425 



was not even a trace of neural crest derivates. They considered these results 

 as typical "activations" {cf. p. 391). 



The technique was approximatively the same in Okazaki's operations (1955). 

 He used Triturus pyrrhogaster middle and posterior pieces of the archenteric roof 

 (neurectoblast included), treated for hours with ethanol at two temperatures; 

 — 18" C and 5^ C, and cultivated in sandwiches. The interest does not lie so 

 much in the nature of the inductions, which were all, as has been expected, of the 

 acrencephalic type, as in their numerical incidence. Treatment at — 18° C 

 provokes only a few inductions (5 to 12%), while at 5° C they are numerous (72%). 

 The question now is whether the first procedure simply inactivates an inducing 

 property resistant to death, or whether ethanol suppresses this property which 

 existed in vivo, but also causes, at temperature above 0° C, a secondary inducing 

 property to appear de novo. The author is in favor of the second alternative, his 

 main argument being that the succession of the two treatments causes the inducing 

 property to reappear. Moreover, the inductive ability obtained by ethanol at 

 5° C is not annihilated by being placed for a time in ethanol at — 18'" C. As a 

 corroborating argument, it has been shown that treatments which do not ap- 

 preciably denature the proteins, such as freezing by solid CO^-ether mixture 

 (plus I day storage at — 18' C), or freezing 3-5 min. in a C02-ethanol mixture 

 (plus thawing in Holtfreter's solution), only suscitate weak inductive capacity, 

 if any. Thus, the cold ( — 18° C) ethanol is thought to annihilate the power of 

 induction which existed in the living explant; warmer (5° C) alcohol evokes a 

 new inducing property. 



This conclusion is perhaps too narrow. The possibility exists that refrigeration, 

 used alone or combined with ethanol treatment, only reduces the inductive power 

 by some condition which prevents the inducing agent from leaving the cells. 

 Relative re-heating or longer alcoholization could remove such a physical block, 

 but evidently can also evoke a supplement of inducing factors. Whatever it may 

 be, it is not in the interest of our analysis to assert, without pertinent reasons, 

 the absence of a relation between normal inducers and those which are revealed 

 by an alteration of some inductor. 



Several other chemicals have been found to modify the induction process or to cause 

 neuralization. In 1944, Brachet mentioned (p. 389) that, although numerous substances 

 were inactive (cresyl blue, dinitrophenol, uric, hippuric, lactic, phenacetic, and oleic 

 acids), a variable amount of positive results could be obtained by using methylene blue, 

 several polycyclic hydrocarbons, benzopyrene, methylcholanthrene, auxin and hetero- 

 auxin, i, 2, 5, 6-dibenzenthracene-endosuccinate. This substance' has been again shown 

 by Shen (1942) to be active when added simply to the standard medium: it elicits the 

 ectoblast brain-like masses, probably acrencephalic, without any trace of mesoblast. 

 Trypanblue, now largely used to cause cardiac and other anomalies in mammalian 

 embryos, is effectively teratogenic on amphibian eggs, and somewhat analogous in its 

 action to LiCl (Waddington and Perry, 1956). 



The effects of tenso-active substances, especially sodium oleate and linoleate have been 

 explored by Gothic (1950), but the rather limited results may be accounted for by a 

 cytolyzing effect. 



^ For the absorption of carcinogenes in Urodeles embryos, see Waddington and Goodhart 



(1949)- 



Literature p. 483 



