218 EXAMINATION AND PRESERVATION MEDIA. 



In order to render it inoffensive to fresh tissues it must have 

 dissolved in it substances of similar divisibility to those 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. 

 Now cell contents are a mixture of colloids and crystalloids ; conse- 

 quently, in order to reduce osmotic processes to a minimum, it is 

 necessary that the examination medium contain a due proportion 

 of both crystalloids and colloids. By adding, for instance, white of 

 egg to salt solution this end may be in some measure attained ; and, 

 as a matter of fact, the liquids recommended as " indifferent " are 

 generally found to contain both crystalloids and colloids. Liquids 

 thus composed, in which tissue-elements are in osmotic equilibrium 

 that is, neither swell nor shrink -are said to be isotonic to the tissues ; 

 whilst those in which they shrink are called hypertonic, and those in 

 which they swell hypotonic. Solutions of common salt, in different 

 concentrations, form the base of the most commonly employed 

 isotonic liquids. For marine Invertebrates, sea-water is generally 

 isotonic. 



402. 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. 



RINGER'S solution, much used in physiology, consists of sodium 

 chloride 0-8 parts, calcium chloride 0-02, potassium chloride 0-02, 

 sodium bicarbonate 0-02 and water 100 (with or without 0-1 dex- 

 trose). 



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 HAMBURGER, 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, 1896, pp. 504 and 511) takes for 

 erythrocytes about 1 per cent, sodium chloride. 



DEKHUYZEN (Onderz. Phys. Lab. Leiden., 1900, p. 149) takes for 

 blood of Rana 0-8 per cent. 



For Selachians, MUSKENS (Tijd. Nederb. Dierk. Ver., 1894, p. 314) 

 finds 2J per cent, right ; and RODIN (Comptes Rend.. 1900, p. 1009) 

 1*5 to 2-6 per cent., according to the species. 



ENGELMANN (Deutsch. med. Wochenschr., xxix, 1903, p. 64) finds 

 that 0-9 per cent, is isotonic with human blood-serum, and 0-64 per 

 cent, for red blood corpuscles of the frog. 



KRONECKER'S " Artificial Serum ' (from VOGT et YUNG, Traite 



