358 CHAPTER XXVII. 



obstruction to the processes of cell-division, and are useful, 

 but their action as anaesthetics is inconstant. 



Indifferent Media. One per cent, salt solution, iodised 

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

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

 studied for a long time in these media (PEREMESCHKO, Ardi. 

 f. mik. Aiiat., xvi, 1879, p. 437), 



Small and transparent aquatic organisms, such as larvas of 

 Diptera, small specimens of Clepsine and Nephelis, etc., may 

 be studied alive in a reversible compressorium. The vege- 

 table kingdom also affords some good objects, for which see 

 the botanical treatises. 



For the processes of staining living cells, which are often 

 important aids to study, see 201. 



646. 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 solu- 

 tion 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 ] 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 ( 391) useful 

 as an examination medium. A little solution of dahlia may 

 be added to it. 



