SOME MICROOHEMICAL REACTIONS. 279 



dictates ; and of course other examination media than solution 

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

 methyl-green-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 CAENOY 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. 



602. Some Microchemical Reactions. Methyl green is a test 

 for nuclein, in so far as it colours nothing but the nuclein 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 suggestions are 

 taken from CAENOY, 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. 



Nuclein is distinguished from the lecithins and from albu- 

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

 weak mineral acids, such as Ol 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 carbonate 

 of potash and biphosphate of soda. In the presence of 10 

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

 tinous mass, or even, as frequently happens, dissolves entirely 

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

 in situ in the nucleus) in the usual laboratory digestion fluids. 



The solvents of nuclein that are the most useful in practice 

 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 

 employed in solutions of 40 to 50 per cent, strength. If it be 

 desired to remove all the nuclein from a nucleus, the reaction 

 must be prolonged sometimes to as much as two or three days, 



