42 FIXING AGENTS. 



very high degree of penetration ; and, in point of fact, iodised serum, which 

 is generally employed as an " indifferent liquid," that is, one which is 

 supposed to exert no action whatever on tissues, is, in reality, a feeble 

 hardening agent, and forms a most admirable fixing agent for delicate 

 tissues. It is so classed by Ranvier (see Iodised Serum, 349, 496). 

 KENT (Manual of the Infusoria, 1881, p. 114, Journ. Roy. Mic. Soc. (N.S.), 

 iii (1883), p. 730), has found it to act in a manner almost identical with osmic 

 acid, and in some instances even more efficiently (for fixing Infusoria). His 

 instructions are as follows : " Prepare a saturated solution of potassic iodide 

 in distilled water, saturate this solution with iodine, filter, and dilute to a 

 brown-sherry colour. A very small portion only of the fluid is to be added 

 to that containing the Infusoria." 



Or you may use the solution of LUGOL, of which the formula is as follows : 



Water 100 parts. 



Iodide of potassium ... 6 



Iodine 4 



Iodine certainly kills cells very rapidly, without deforming them. Perso- 

 nally I have found it very useful for the examination of spermatozoa. 

 Unfortunately I am not acquainted with any nuclear stain that will work 

 well with it. 



