THE DIPLOID CHROMOSOME COMPLEXES OF THE PIG 159 



2. Place small or finely teased pieces of fresh tissue into cold 

 Flemming's (strong) solution to which a little urea (one-half per 

 cent) has been added. When the bottles of fluid are surrounded 

 with ice the temperature of the fixative is about four degrees 

 Centigrade. Allow the tissue to remain in the fluid twenty to 

 twenty-four hours. (Flemming's weak solution was also used 

 successfully. See below.) 



3. Wash in water for about twenty-four hours. 



4. Dehydrate by very gradual steps. 



5. Clear from 95 per cent alcohol in cedar oil followed by xylol. 



6. Imbed in paraffin. 



7. Cut the sections ten micra thick. 



8. Bleach the sections for from one to twenty-four hours in 

 peroxide. 



9. Stain with iron alum haematoxylin. 



This method has never failed to give good results and has 

 been used on over sixty lots of material taken from seven mam- 

 malian species. The same results were obtained on testes, ovary 

 and embryo. 



I have studied testes obtained at the time of castration from 

 pigs about four or five months old representing three breeds, 

 Berkshire, Jersey red and Poland china. The first two were ob- 

 tained at Philadelphia and the last from Kentucky. None of 

 the pigs were thoroughbreds, although I was told that the Poland 

 china was 'nearly so,' whatever that may mean. Forty-two 

 embryos of various sizes have been fixed either entire or teased. 

 The fixation in the case of those killed without teasing is as good 

 as in the shredded embryos. Only a few of the specimens from 

 this lot of material have been studied, since it was thought better 

 to initiate this study with thorough observations on a small 

 number of animals. It has been a matter of considerable regret 

 that I have been unable to study any ovarian chromosomes. I 

 recently prepared embryonic ovaries taken from foetuses about 

 half grown, but all the material proved worthless, as the chromo- 

 somes were badly clumped. The only explanation I have to 

 offer for this is that the system in the Philadelphia slaughter- 



