SOME M1CEOCHEMIOAL REACTIONS. 327 



solution, may of course be used, and in some cases doubtless 

 should be preferred. Other stains, too, such as Bismarck 

 brown or Delafield's haematoxylin, may be used as occasion 

 dictates ; and of course other examination media than solution 

 of Ripart may be employed. But, for general purposes, the 

 methyl-greeii-osmium-and-Ripart's-medium method gives such 

 good results, and is so very convenient, that it may well be 

 called the classical method for the study of fresh cells. I 

 think great credit is due to CARNOY for his frequent insistence 

 on the excellence and handiness of this method. 



Other fixing agents and stains that are applicable to this 

 kind of work will be found discussed in the course of the 

 following paragraphs. 



636. Some Microchemical Reactions. Methyl green is a test 

 for chromatin, in so far as it colours nothing but the chro- 

 matin in the nucleus. It is, however, not a perfect test, for 

 the intensity of the coloration it produces varies greatly in 

 different nuclei, and may in certain nuclei be extremely weak, 

 or (apparently) even altogether wanting. In these cases 

 other tests must be applied in order to establish with certainty 

 the presence or absence of that element. The following sug- 

 gestions are taken from CARNOY, who is, I believe, the only 

 writer on the zoological side, at all events who has insisted 

 on the necessity of applying microchemical methods in a 

 systematic manner to the study of cells. 



Chromatin is distinguished from the lecithins and from 

 albuminoids by not being soluble, as these are, in water and 

 in weak mineral acids, such as 0*1 per cent, hydrochloric acid. 

 It is easily soluble in concentrated mineral acids, in alkalies, 

 even when very dilute, and in some alkaline salts, such as car- 

 bonate of potash and biphosphate of soda. In the presence of 

 10 per cent, solution of sodium chloride it swells up into a 

 gelatinous mass, or even, as frequently happens, dissolves en- 

 tirely (Biol. Cell., pp. 208-9). It is only partially digestible 

 (when in situ in the nucleus) in the usual laboratory digestion 

 fluids. 



Tlip solvents of chroraatin that are the most useful in prac- 

 tice are 1 per cent, caustic potash, fuming hydrochloric acid, 

 or cyanide of potassium, or carbonate of potash. These last 

 generally give better results than dilute alkalies. They may be 



