78 SEVENTEENTH REPORT. 



adapted to the more heavily volk-laden egg of Cryptobi-ancluis. The 

 fonniihi is as follows: 



Potassium bichromate 1 gram 



Glacial acetic acid 2.5 cc. 



Formalin, Schering's 5 cc 



Water 97.5 cc. 



Eggs fixed in this solution cut better than those fixed in Tellyes- 

 nicky's solution, but the yolk was still slightly brittle. By cutting 

 thick sections (20 microns) at a high room temperature crumbling 

 of the yolk could usually be avoided. The cell structure was well 

 preserved. 



The results with these three fixing solutions pointed to the use 

 of formalin, in combination with a small proportion of potassium 

 bichromate and acetic acid, as a satisfactory fixing solution for 

 the frog's egg. The following formula was tested and proved en- 

 tirely satisfactory: 



Potassium bichromate 0.5 gram 



Glacial acetic acid 2.5 cc. 



Formalin, Schering's 10 cc. 



Water 87.5 cc. 



The sections should be cut 15 to 20 microns thick, in a warm room. 



The envelopes are most easily removed before fixation, but care 

 must be taken not to disturb the egg by rough handling, since this 

 may result in a rearrangement of internal structures. Tn the gas- 

 trula stage the thin septum between blastocoele and gastrocoele is 

 easily broken down. For this reason, and because one may find it 

 inconvenient to spend time in removing the envelopes when preserv- 

 ing eggs, it is desirable to choose a fixing solution that will permit 

 of the eggs being killed with envelopes intact. 



With fresh material, with material preserved in formalin only, or 

 material preserved in a bichromate-formalin-acetic solution contain- 

 ing not more than 0.5% bichromate, the envelopes may be easily re- 

 moved by holding the eggs in the palm of the hand, or on moist 

 filter paper, and cutting the envelopes with a sharp scalpel. If the 

 material has been fixed in a solution containing more than 0.5% 

 bichromate, it is necessary to remove the envelopes with sharp 

 needles, and this is a difficult and tedious process. 



Eggs fixed in a bichromate-acetic solution should be rin.sed in 

 water, and washed in frequent changes of weak formalin (5%) 

 for several days, until the fomialin is no longer discolored. If the 



