318 niArruii \\vi. 



These reagents cause no obstruction to the processes of cell- 

 division. 



Indifferent Media. One per cent, salt solution, iodised 

 serum, syrup, cold water (+ 1C.), and warm water (35 - 

 40 0.). The tail may be excised from the living animal and 

 studied for a long time in these media (PEKEMESCHKO, Arch, 

 mik. Anat., xvi, 1879, p. 437). 



For the processes of staining living cells see 208. 



645. Study of Fresh and Lightly Fixed Cells. So-called 

 " indifferent " 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 pre- 

 paration 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. 



HENKINQ (Zeit. wiss. Mik., viii, 189 J, 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 grin. 



