1915] Johnson: The Cultivation of Tisfiues from Ampliibians 



motion from the .surface away from, to the surface 

 attached to the glass. Lack of dark granules here of 

 some kind made it very difficult, in fact impos-sible. to 

 trace the current of the protoplasm further, yet the above 

 fact, coupled with the fact that always just behind the 

 enlarged bulb the fibers are thinner than at any other 

 point, seemed to show very definitely that there is an out- 

 pulling of nerve tissue rather than an out-pushing (see 

 figs. 1 and 2). 



Another very interesting feature is the extreme fre- 

 quency with which ti.ssues of the head region formed 

 gill-like structures. These thumb-like processes are very 

 similar to the regular gill structures them.selves, although 

 generally smaller and often not as regular in outline. 



A modification of technique generally used seems to 

 me to be quite essential in order to get a greater per- 

 centage of immediate active outgrowths. This modiii- 

 eation is the tran.sition drop. I have often noticed that 

 media in which tissues were placed failed to coagulate, 

 particularly close around the ti.ssue itself, although I 

 knew the media to be coagulable previous to putting on 

 the cover-slip. Failure to solidify around the tissue is 

 always detrimental to outgrowth, at least slowing it down 

 considerably as has been demonstrated by others, and 

 verified in my own experiments many times. This failure 

 to become solid I found to be due to the fact that no 

 matter how small the instrument used upon which I 

 transferred tissuas from Ringer's solution to serum mix- 

 ture on the cover-glass, there was always a considerable 

 film of the solution transferred with tissues at the same 

 time to the serum, thus allowing the tissue to float some- 

 what loosely rather than having the necessary solid 

 support. To overcome this difficulty the tissue was 

 always placed in a drop of .same serum mixture where 

 it was rinsed thoroughly of Ringer's solution and from 

 here transferred to the drop of serum mixture on the 

 cover-glass. In ease of retransference of tissues, indi- 

 vidual drops have to be used in order to prevent the 

 infection of one tissue by another. The only objection 



Fig. 1. Outline 

 of one nervo fiber as 

 vieweil muler oil- 

 immersion lens. 



