PREVENTIVE MEDICINE 207 



tion by liberating an excess of chlorine atoms in the solution. An 

 alcoholic solution of perchloride of mercury has a germicidal action 

 that is practically limited to the action of the alcohol, since little 

 ionisation takes place in the presence of the alcohol and the mole- 

 cules remain intact or nearly so. The salt is said to preserve its dis- 

 infectant powers in fats or oils, as it is only feebly soluble in them 

 and therefore leaves them readily for the fluids of bacteria 

 (Cushny). 



Since perchloride of mercury is germicidal by virtue of the 

 affinity of the free mercury ions for albuminous material, it follows 

 that if a solution of the salt is brought into contact with organic 

 matter containing albumin much of its strength will be expended 

 upon the harmless substance, while the bacteria may escape its 

 action. Its use as a disinfectant of animal excreta is still further 

 contraindicated owing to the presence of the potassium and sodium 

 chlorides. Perchloride has a corrosive action on metals, the 

 mercury becoming deposited. It is therefore useless as a dis- 

 infectant for instruments or for disinfecting metal work, such, for 

 instance, as the iron or brass work of stalls and other fittings. Not 

 only does the mercury spoil the metal but, being deposited, is not 

 available for action on the bacteria. 



Muir and Ritchie* state that the perchloride in a strength of 

 1-100 will kill anthrax spores in twenty minutes, although an hour's 

 exposure to 1-1000 has no effect. According to these authorities 

 the best results are obtained by the addition to the sublimate of '5 

 per cent, of sulphuric or hydrochloric acid, when the spores will be 

 killed by a seventy-five minutes' exposure of a 1-200 solution. With 

 regard to the vegetative forms, they go on to say that anthrax 

 bacilli in blood will be killed in a few minutes by 1-2000, in bouillon 

 1-40,000, and in water 1-500,000. " Generally speaking, it may be 

 said that a 1-2000 solution must be used for the practically instant- 

 aneous killing of vegetative organisms." 



Corrosive sublimate is conveniently put up in tablet form so 

 that dilutions of any strength can be made with accuracy and with- 

 out delay. Common salt and some colouring matter, usually 

 eosine or methylene blue, are incorporated. The former is added 

 to increase solubility, but as the presence of sodium chloride in 

 the solution tends to hinder ionisation of the mercuric salt, the 

 amount of salt added to the tablet should be limited to the minimum 

 required. The salts are usually combined in equal proportion. 

 Tartaric acid is added to increase the electrolytic dissociation when 

 in solution. Colouring matter is added to give a distinctive colour 

 * Manual of Bacteriology, London, 1919, p. 171. 



