EXAMINATION AND PRESERVATION MEDIA. 269 



389. Theory of Indifferent Liquids. In order to render 

 water inoffensive to such tissues as these it must, firstly, have 

 dissolved in it some substance that will give it a density 

 equal to that of the liquids of the tissue, so as to prevent the 

 occurrence of osmosis, to which process the destructive action 

 of pure water is mainly due. Salt solution is a medium sug- 

 gested by this necessity. But salt solution by no means 

 fulfils all the conditions implied in the notion of an " indif- 

 ferent " liquid. In so far as it possesses a density approach- 

 ing to that of the liquids of the tissues, one cause of osmosis 

 is eliminated ; but there remains another, due to the difference 

 of composition of the liquids within the tissues and that with- 

 out. Cell contents are a mixture of colloids and crystalloids ; 

 salt solution contains only a crystalloid, whose high diffusi- 

 bility causes it to diffuse over into the colloids of the tissues. 

 In order to reduce the consequent osmotic processes to a 

 minimum, it is necessary that the examination medium con- 

 tain, in addition to a due proportion of salt or other crystal- 

 loid, also a due proportion of colloids. By adding, for 

 instance, white of egg to salt solution this end may be 

 attained ; and, as a matter of fact, the liquids recommended 

 as indifferent are found invariably to contain both crystal- 

 loids and colloids. Thus (as stated by FREY) vitreous humour 

 contains 987 parts of water to about 4'6 of colloid matters 

 and 7*8 of crystalloids (common salt). In 1000 parts of 

 liquor amnii are contained about 3*8 parts of colloid matter 

 (albumen) , 5 '8 of salt, and 3*4 of urea. In blood-serum, 

 8*5 of colloids and 1 of crystalloid substance are found. 



390. Salt Solution (" normal salt solution/' " physiological 

 salt solution"). 0'75 per cent, sodium chloride in water. 

 CARNOY recommends the addition of a trace of osmic acid. 



According to LOCKE (Boston Med. Surg. Journ., 1896, p. 514) there 

 should be added to salt solution (which to be isotonic should contain, 

 according to HAMBUEGEE, 0'9 to 1 per cent, of salt) 0*01 per cent, 

 chloride of potassium and 0'02 per cent, chloride of calcium, in order to 

 obtain an indifferent liquid. MALASSEZ (C. R. Soc. BioL, iii, |896, 

 pp. 504 and 511) takes for erythrocytes about 1 per cent, sodium chloric 



391. PICTET'S Liquid (Mitth. Zool. 8 tat. Neapel, x, 1, 1891, 

 p. 89). 5 to 10 per cent, solution of chloride of man- 



