422 GERMINAL ORGANIZATION INDUCTION PHENOMENA 4 



have not acquired any apparent acrogenetic ability. The proportion of neural tubes, 

 neuroids, and even tails, has been appreciably increased. Thus, the uniformity goes hand 

 in hand with some alterations of the morphogenetic potential. 



The effect of disaggregation on early dorsal lips was also tested, with the resulting 

 impression that the controls — which showed only modest reactions — "did not feature any 

 more complete or successful inductions than the experiments" (her p. 31). Two reaggregated 

 cell masses from the dorsal lip were also successfully implanted into the ventral half of a 

 young gastrula. One induced only a spinal cord, the other a notomerit. 



It may be concluded that disaggregation does not suppress the inducing capacity 

 of the blastoporal lip (as already seen by Holtfreter, 1944b) nor of the archen- 

 teron roof but interferes to a certain extent with the quality of the process. 

 Except for the anterior third of the roof — where the existence of acrogenetic 

 factor(s) is not surprising — this treatment does not produce the change so 

 characteristic of heat [supra) and other agents (infra). 



A close relation exists between the preceding results and the effects which Yamada (ig5oa) 

 described after "shock-treatment" by ammonia on explants of the ectoblast and of the 

 ventro-marginal zone; his experiments practically amount to a temporary disaggre- 

 gation of the cells, including appreciable cytolysis. Consequently, the neuralization of 

 ectoblast explants has only a confirmative value. However, it can be emphasized that the 

 differentiation of the ventral marginal zone is distinctly enhanced. Instead of blood islands, 

 blood vessels, mesothelium and pronephric tubules, it yields notochord, muscle and the 

 same kidney tubules. 



A further analysis of the "dorsalization" exerted by a:nmonium on the ectoblast and 

 on ventral marginal zone has lead Karasaki (1957) and Ogi (1958a, b) to consider other 

 cytolytic and disaggregating agents. The former author has shown that disaggregation 

 does not necessarily bring forth dorsalization nor acrencephalic induction. For example, 

 mild treatment with ethanol disaggregates the cells, but does not exert any morphogenetic 

 effect. To get this action, it seems necessary that the agent should cause solation of the 

 cell endoplasm. 



The second author has first used a drug known for its activity on morphochoresis, 

 sodium thyocyanate (p. 349). It causes acrencephalic structures to appear in the ectoblast, 

 a rather banal and perhaps precytolytic effect. In isolated ventral mesoblast, NaCNS 

 suscitates notochord, muscles even otocysts. Such a deutogenic modification may also 

 be obtained by lactic acid, sodium iodide, urea, hydrochloric acid, zinc chloride. Ogi 

 now explored which kind of induction would exert on normal ectoblast fragments of the 

 ventral marginal zone submitted to these various reagents to the point where disaggre- 

 gation begins. It turned out that most of them induced deutomerit structures, except 

 HCl and ZnClj, who are acrogenic. Thus, both kinds of inducing "potencies" may be 

 suscitated in the same presumptive ventral mesoblast, by using appropriate means. 



As other inorganic substances which exert appreciable effects on morphochoresis, 

 we must mention : boric acid, which perturbates the formation of the notochord 

 in toad eggs (Takenchi, 1958) ; lithium chloride, important enough to deserve the 

 next paragraphs; acidification of the standard (Holtfreter's) solution (Kawakami 

 and Okano, 1955); formalin, which combines with amine groups and thereby 

 reduces the activity of proteolytic enzymes (Lallier, 1950); zinc salts which cause 

 expansions of the ectoblast cytoplasms and increase sensibility to the same 

 enzymes (Lallier, 1955); sodium azide, a depressive agent which seems to disso- 

 ciate metabolism of maintenance from that of differentiation and growth (Hall and 

 Moog, 1948). 



