NUTRITION OF PARASITES AND SAPROPHYTES 139 



" original one from the water supply, and then a number of second- 

 ary ones around the various primary cases due to carelessness 

 in or lack of proper disinfection. Boiling the water or milk and 

 thoroughly cooking the food kills the germs, but the wiser way 

 is to prevent the primary infection. In this respect the public 

 authorities should see to it that the water supply is kept pure both 

 by cleanliness of the water shed, and by building proper nitration 

 plants where a supply of pure artesian water is not available. 



