424 



GERMINAL ORGANIZATION INDUCTION PHENOMENA 



The procedure used by Barth and Graff (1943) is an attempt to separate and 

 concentrate the inducing substance. They gathered parts of the whole archenteric 

 roof, extracted with 5°o NaCl at 5° C, fihered the extract and either added 

 Hohfreter's solution or dialized. In both cases they obtained a precipitate which 

 they injected into the blastocoele. Moreover, the material first extracted by 

 NaCl was re-extracted by 0.05 N NaOH and the filtered product precipitated 

 by acetic acid. This preparation was also injected into the blastocoele. Its inductive 

 activity proved largely superior to the saline extract. It consisted sometimes of 

 short neural tubes, sometimes in multi-layered, brainlike vesicles. The result is 

 supposed to reveal the importance of the protein component of the archenteric 

 roof 



01F.(5MNTPL2 



OLE GIANT 

 PL.1 



Fig. 82. Same experiment as in Fig. 80, but with an inductor killed with ethanol. The 

 relation of the brain to the inductor, its retina-like structure in the zone of closer contact, 

 and the absence of mesenchyme are still more striking. The acrencephalon is completed by 

 two olfactory placodes, a giant, half-circle one Vv'hich is cut twice, and a small one, at the 

 tip of the brain. Br{ret). - the diencephalon partly transformed into a retina; impl. - the dead 

 implant; olf.pl. - the apical olfactory placode; olf. giant PI. (i, 2) the two sections of the 

 same giant placode. From Rollhauser, 1953. 



Ethanol has been used by several authors to stop life processes in the "organizer" 

 (Holtfreter, 1934b). The morphogenetic effect of this treatment is similar to that 

 of heat, and especially pertinent (Fig. 82) in Rollhauser's work (1953). It has 

 become customary to state that "denatiiration" of the proteins contained in the 

 implant favors the induction of an acrenceph: Ion, but this is probably an over- 

 simplification. Typical reactions were described by Hori and Nieuwkoop (1955) 



who placed in sand 

 4 h. with 70% ethr 

 they obtained rail 

 diencephalon, cor. 

 and olfactory pln^ 



-I'ccoi of the r^rchen^eron roof treatc"' fir "^,0 min. to 



' icli reacts c intensely, 



.'zable as tciciccpaalon, and 



;i dered as retina and tapetum, 



. ;".enchvme was striking; there 



