THE AMPHIBIAN GERMINAL VESICLE 



175 



A study of the action of fixatives on the vesicle Is very profitable. Isolate 20 to 

 30 full-sized vesicles in N-medlum and, while observing them under low- magnification of 

 the microscope (under elevated coverslips) add singly such fixatives as Bouin's, i^^ 

 formalin, satizrated HgClp in water, etc. Immediate changes in size and consistency of the 

 vesicle should be noted. Since Bouin's contains an acid, follow the Bouln- fixation with 

 some alkaline treatment to attempt to counteract the acid factor in this fixation. 



A study of the fixed germinal vesicle raises the legitimate question as to how far we 

 may assume that fixed material accurately represents the structures of the living germinal 

 vesicle. Probably the more accurate picture is a composite one, arrived at by the study of 

 both fresh and fixed material. 



C. IONIC EFFECTS 



A visible Iso-electric point can be demonstrated passing through the germinal vesicle 

 by the addition, to one side of the coverslip, of a small drop of dilute BCl. If a slow 

 reaction is desired, use O.OOIN-HCI; if a fast reaction is desired, use O.OOJN-HCl. The 

 germinal vesicle is negatively charged. Note the Brownlan movement of granules. The dif- 

 fusion of weak acids through the germinal vesicle gives an effect known as the "Eing 

 Phenomenon". As proteins within the vesicle reach the iso-electric point (I.E. P., here- 

 after) they become insoluble and appear as floccules. The size of the floccule Is relative 

 to the speed of the acid penetration. If penetration is fast, the floccules will be small; 

 if penetration is slow, they will aggregate and be large. Observe the fusion of micelles 

 to build up the so-called "llnln reticulum". 



The chromosomes will appear and become distinct -only when the solution Immediately 

 aroimd reaches the I.E. P. of the chromosomes. Watch the I.E. P. passing to the center of 

 the germinal vesicle and the subsequent swelling of the outer colloidal area, which be- 

 comes positively charged and reverses Its reaction. 



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