Method XVIII 



lOI 



times their volume of Zenker's fluid (B). After remaining in 

 this for 12—24 hours, the embryo should be washed for 4-6 

 hours in several changes of distilled water and then preserved 

 in 70 or 80 per cent, alcohol. The alcohol should be changed 

 after the first 24-48 hours. 



If the specimen is to be dehydrated and imbedded immedi- 

 ately, it should, after 2 to 6 hours' washing in the water, be 

 placed in an iodine solution (IV, 2, p. 32) 6-8 hours, or long 

 enough to remove the crystals resulting from the action of the 

 bichloride of mercury. Otherwise the crystals will eventually 

 be dissolved out by the alcohol in which the specimen is pre- 

 served. 



3. Foetuses of from 2 to 4 months' should be treated in 

 still a different way. They are rather large to insure good fixa- 

 tion throughout if placed whole in either of the two fluids used 

 above. The specimen should be divided, or, if it is desired to 

 make a detailed cell study of any of its organs, those organs 

 should be removed and placed separately in the fluid. If, how- 

 ever, as is often the case at the time a specimen is obtained, it 

 is more convenient to place it in the fluid whole, Lavdowsky's 

 mixture (C) is recommended as one of the best in that case. 

 Use a copious amount of the fluid and open the body cavity 

 before placing the specimen in it. This fluid will produce very 

 little distortion of the specimen, and its penetrating power is 

 such that it will fix the tissues fairly well for general histologi- 

 cal purposes. It is not recommended for cytological work. 

 The specimen may remain in the fluid indefinitely. 



'TABLE GIVING APPROXIMATE LENGTH AND WEIGHT OF FCETUSES AT DIFFERENT 

 MONTHS OF GESTATION. 



Digitized by Microsoft® 



