CHAPTER XXVI. 293 



644. Study of Fresh and Lightly Fixed Cells. So-called " in- 

 different ' liquids must not be believed to be without action on 

 nuclei. Iodised serum, salt solution, serum, aqueous humour, 

 lymph, better deserve the name of weak hardening agents. Between 

 these and such energetic hardening agents as Flemming's mixture 

 come such light fixing agents as picric acid or very dilute acetic acid. 

 These it is whose employment is indicated for the study of fresh 

 isolated cells. 



A typical example of this kind of work is as follows : Tease out 

 a piece of living tissue in a drop of acidulated solution of methyl 

 green (0-75 per cent, of acetic acid). This is a delicate fixing agent, 

 killing cells instantly without change of form. Complete the fixation 

 by exposing the preparation for a quarter of an hour to vapour of 

 osmium, and add a drop of solution of Ripart and Petit and a cover. 



Or you may fix the preparation, after teasing, with vapour of 

 osmium for half a minute-to two minutes, then add a drop of methyl 

 green, and after five minutes wash out with 1 per cent, acetic acid, 

 and add solution of Ripart and Petit and cover. 



Or you may kill and fix the cells by teasing in solution of Ripart 

 and Petit (to which you may add a trace of osmic acid if you like), 

 and afterwards stain with methyl green. 



I have found Pictet's chloride of manganese ( 403) useful as 

 an examination medium. A little solution of dahlia may be added 

 to it. 



HENKING (Zeit. wiss. Mik., viii, 1891, p. 156) recommends a 

 liquid composed of- 



Water ...... 80 c.c. 



Glycerin ...... 16 



Formic acid ..... 3 



Osmic acid of 1 per cent. ... 1 



Dahlia ...... 0-04 grm. 



Other fixing agents, such as picric acid or weak sublimate solution, 

 may of course be used. Other stains, too, such as Bismarck brown, 

 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 be called a classical method for the study of 

 fresh cells. 



645. Some Microchemical Reactions. Methyl green is a test for 

 chromatin, in so far as (with fresh cells) it colours nothing but the 

 chromatin in the nucleus, see 276. It is, however, not a perfect 



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