CHROMATIN, ANIMAL CHROMOSOMES, NUCLEOLI 269 



surface, which becomes very brittle in the higher grades of alcohol, 

 are not broken off and the best preserved cells lost. 



For the preservation of testicular material, Oguma {Jour. Col. 

 Agri., Hokkaido Imp. Univ," xvi, 1927, p. 203) uses Hermann's fluid 

 (containing about 1 per cent, urea) warmed to about 40° C, and fixes 

 for a few hours. Painter, and many others, have used Rouin-Allen 

 followed by tlie anilin and wintergreen oil method of imbedding. For 

 embryonic divisions, Hance recommends strong Flemming (witli 1 

 per cent, urea added) chilled with ice (§ 626). Oguma prefers warm 

 Hermann's fluid. Amniotic divisions in six to ten-day-old embryos 

 are excellent for somatic chromosomes. 



631. Reptilian Chromosomes. The methods employed for 

 mammals will be found good. Nakamura {Mem. Col. Sci., Kyoto 

 Imp. Univ., Scries B, Iv, 1928, p. 1) has used the following modifica- 

 tion of Champy's fluid which is highly recommended, also, by 

 Matthey {Rev. Suisse Zool., xxxvii, 1931, p. 117) : 2 per cent, 

 osmic acid. 3 parts ; 1*6 per cent, chromic acid, 6 parts ; and 6 per 

 cent, potassium bichromate, 4 parts. Tissue is fixed in this 

 mixture for twenty-four hours, washed for the same length of 

 time, slowly dehydrated, cleared in cedar oil, then in chloroform, 

 and imbedded. Sections are bleached in hydrogen peroxide in 

 50 per cent, alcohol and then placed in Chura's fluid for twelve to 

 twenty-four hours, to dissolve out cytoplasmic inclusions and to 

 render the chromosomes more easily stainable. 



632. Amphibian Chromosomes. Except for maturation divi- 

 sions in oocytes, Bouin- Allen is excellent for germinal and somatic 

 divisions. Recently, some Japanese cytologists, e.g., Making, 

 Jou7\ Fac. Sci., Hokkaido Imp. Univ., ii, 1932, have found that 

 either Benda's or Flemming's solutions are excellent if the acetic 

 acid is reduced or omitted. For the meiotic divisions in mature 

 eggs. Making {Jour. Fac. Sci., Hokkaidic Imp. Univ., Zool., iii, 

 1934, p. 117) uses a saturated solution of mercuric chloride con- 

 taining about 1 per cent, of acetic acid. Eggs are fixed for ten 

 to fifteen minutes and washed in 70 per cent, alcohol. The 

 gelatinous envelopes shoidd be removed from the eggs before 

 fixation. If the eggs have been in water for a little while, this 

 can be easily done with a pair of scissors. Freshly laid eggs, or ones 

 taken from the oviduct, are preserved and washed first and are 

 then placed in a 10 per cent, solution of formol This causes 

 the membranes to become brittle, and they may now be removed 

 with needles. After dehydration, cedar oil is used for clearing, 

 and then the eggs are placed in a mixture of creosote and toluol 

 (equal parts), where they are left for about thirty minutes. The 

 creosote is washed out with toluol and the eggs are imbedded. 



633. Teleost Chromosomes. Iriki recommends Champy's fluid 

 {Froc. Imp. Acad., Tokyo, viii, 1932, p. 262). Making {Cytologia, 

 V, 1934, p. 155) finds that Champy's works well with spermatocyte 

 stages, but for spermatogonial divisions Benda's fluid diluted 



