STERILISATION OF WATER 599 



the flasks with a sterile pipette. Any likely vibrios isolated 

 must have its cultural and biological reactions investigated and be 

 tested for the agglutination and Pfeiffer reactions with a high-grade 

 cholera serum. 



On the survival of the typhoid and cholera organisms in water, 

 see pp. 360 and 437 respectively. 



Ice and ice-creams may be examined by methods similar to those 

 used for water, the material being first melted at a low temperature. 

 Some of the fluid should also be centrifuged and the deposit 

 examined microscopically for gross contamination. 



The infection in typhoid fever and cholera, and perhaps 

 also in bacillary dysentery, is perhaps more frequently 

 water-borne than conveyed in any other way. It might 

 be supposed that the acid gastric juice would prevent this, 

 and it may do so in many instances. Experiments by 

 Macfadyen l showed that, whereas in fasting animals, 

 to which suspensions in water of the cholera vibrio were 

 administered, living vibrios pass into the intestine, when 

 the vehicle is milk none could be detected in the intestines. 

 The inference is that when there is no food there is no 

 gastric juice secreted and the organisms are able to pass 

 into the intestine, but when food is present the gastric 

 juice is secreted and the organisms are destroyed. 



STERILISATION OF WATER. This may be done on the small scale 

 by heat, by the use of germicidal agents, or by filtration through a 

 filter (see p. 601). Heat may be applied by simple boiling, or by 

 the use of apparatus in which the water is heated to 65-90 C., 

 and the outgoing hot water is cooled by the ingoing cold water, 

 which itself is thus warmed, thereby effecting economy in fuel 

 (Griffiths' and other sterilisers). The chemical germicides that 

 have been employed are (1) sodium bisulphate, 15 grains to the 

 pint ; (2) Potassium permanganate, sufficient to tinge the water 

 deeply for at least half an hour ; (3) chlorine gas or iodine tablets, 2 

 in both cases the taste of the agent being destroyed by the addition 

 of sodium sulphite ; (4) copper and copper sulphate. Sufficient 

 metal is dissolved from bright copper in twenty-four hours to destroy 



1 Journ. of Anat. and PhysioL, vol. xxi. 



2 Nesfield, Journ. Prev. Med., vol. xiii, 1905, p. 623. 



