WEYSSE. — BLASTODERMIC VESICLE OP SUS SCROFA. 285 



3. Technique. 



In the case of the first uteri which I opened, I followed with some 

 variations one of the methodo which Keibcl ('93) has described in his 

 work on the pig. When the uterus had been removed from the animal, 

 it was cut open along the side opposite the mesometrium and placed 

 in a flat-bottomed glass dish containing Kleinenberg's picro-sulphuric 

 mixture and resting on a black tile. Then, by carefully spreading out 

 the complicated folds of the inner wall of the uterus and gently agitating 

 them, the embryos readily floated out into the fluid, and could be dis- 

 tinguished at once against the black surfi^co of the tile. They were 

 then carefully removed on a spatula to a smaller vessel of the picro- 

 sulphuric mixture, where they remained several hours and were then 

 transferred to 70% alcohol, and after twelve or fourteen hours to 90% 

 alcohol, which was gently warmed and changed several times until all 

 trace of the acid had been washed out. But this method had some 

 minor disadvantages which seemed avoidable ; the action of the acid 

 mixture on the instruments used, and the staining of the hands, were 

 at least undesirable, and to be avoided unless absolutely necessary. 

 Accordingly, in my later work, instead of using Kleinenberg's mixture 

 as a medium for floating out the embryos from the uterus, I employed 

 normal salt solution (0.75% NaCl in water), at a temperature of about 

 40° C. Keibel ('93) says that he did not use this because it is said to 

 injure the embryos, and Bonnet ('84) found that, if embryos lay a long 

 time in this solution, they became swollen. This is doubtless true, if 

 they remain in the fluid as long as is necessary to detach such com- 

 plicated embryos as Keibel worked with, some of which were more 

 than a meter long and greatly folded amongst the plications of the 

 uterine wall. The same may be true for the embryos of the sheep, — 

 upon which Bonnet worked, — which at a corresponding stage of de- 

 velopment closely resemble those of the pig, hut in the case of such small 

 embryos as those which I have been concerned with the very short 

 time during which it is necessary for them to remain in the salt solu- 

 tion has absolutely no effect either on the general form of the embryo or 

 on the histological conditions, as my sections clearly demonstrate. As 

 soon as the embryos were floated out from the uterus, they were at 

 once transferred as before to Kleinenberg's picro-sulphuric mixture. 

 All the embryos which I have studied have been fixed in this fluid. 

 Had my supply of material been larger, I should have employed 

 several other fixing reagents, but my work on young embryos of other 

 mammals, as well as the results of the experiments of other embry- 



