BACTERIA II\r WATER 83 



time and maintained in a cleanly condition. Suction into 

 the tap has been recently emphasised by Dr. Vivian Poore 

 as a cause of pollution. It is liable to occur whenever a tap 

 is left turned on, and a vacuum is produced in the supply- 

 pipe by intermission of the water supply, so that foul gas or 

 liquid is sucked back into the house-pipe. 



One more point requires our attention. It has relation 

 to bacterially polluted water when it has gained entrance to 

 the body. It has been known for some time past that not 

 all waters polluted with disease germs produce disease. As 

 we have before said, this may depend upon the infective 

 agent, its quantity and quality; the body being able in 

 many cases to resist a small dose of poison. It is, however, 

 necessary to infection, especially in water-borne disease, that 

 the tissues shall be in some degree disordered. The per- 

 verted action of the stomach influences the acid secretion 

 of the gastric juice, through which bacilli might then pass 

 uninjured. Particularly must this be so in the bacillus of 

 cholera, which is readily killed by the normal acid reaction 

 of the stomach. Hence, in this disease at least, it is the 

 opinion of bacteriologists that the condition of the mucous 

 membrane of the stomach is of primary importance. Metsch- 

 nikoff has indeed demonstrated the presence of the bacil- 

 lus of cholera in the intestinal excretion of apparently 

 healthy persons, which shows that they were protected by 

 the resistance of their tissues to the bacilli. Further light 

 has been thrown on this question by the researches of Mac- 

 Fadyen, who has pointed out that suspensions of cholera 

 bacilli in water passed through the stomach untouched, and 

 were thus able to exert their evil influence in other parts of 

 the alimentary canal. When, however, cholera bacilli were 

 suspended in milk, none appeared to escape the germicidal 

 action of the gastric juice. The explanation of this is prob- 

 ably the simple one that the stomach reacted with its secre- 

 tion of gastric juice only to food (milk), but simply passed 



