272 GEORGE W. BARTELMEZ 



The formol should be added at the time of using and the mixture 

 warmed to the body temperature. As has been said, this fixa- 

 tion only preserves the external form-relations of the oocytes. 

 Cytologically the microscopic picture is not true to life and, as 

 the photographs show, the nucleus is always more or less plasmo- 

 lyzed. After fixation and washing, the ovary is run up through 

 the alcohols to 95 per cent containing a trace of eosin, then crea- 

 sote is added very gradually during the course of a day or two and 

 the ovary finally studied in pure creasote. The most important 

 factor in avoiding distortions is the gradual clearing. The method 

 involves little shrinkage and the change in shape is within the 

 probable error in measurement and negligible as may be seen from 

 table 1. 



The average shrinkage of twenty oocytes, ranging between 1 

 and 5 mm., was 4 per cent; in no instance was it greater than 5 

 per cent. The shrinkage involved in paraffin imbedding and cut- 

 ting may be judged' from the following: an oocyte of 2.5 mm. be- 

 fore fixation, measured 2.4 mm. in alcohol and 2.3 mm. in par- 

 affin. It was cut perpendicular to the long axis into 221 sections 

 10/i thick. This means a total shrinkage of 11.6 per cent. The 

 eff"ect of the compression in cutting may be judged from figure 

 27, a photograph of a median section of this egg. The two axes 

 shown were nearly equal before cutting. 



To study the blood supply the ovary was injected with a freshly 

 prepared, 5 to 7 per cent solution of Higgins' india ink in physio- 

 logical salt solution (see Evans, '09). After light staining in 

 eosin it was cleared and studied in creasote. 



For cytological control the recent mitochondria methods were 

 used. The most favorable fixative is Benda's 'modified Flem- 

 ming' : 



One per cent aqueous chromic acid 15 cc. 



Two per cent aqueous osmic acid 4 cc. 



Glacial acetic acid 3 drops 



This fixation gives a microscopic picture most nearly resembling 

 the appearance of the living oocytes under the immersion lens; 

 the protoplasm appears as a homogeneous ground substance in 

 which are imbedded granules of various sizes and staining reac- 



