630 MAN AS A CONQUEROR 



posal of sewage from the homes up stream," and in one milk-receiving 

 station "the water used mainly for washing the cooling vats and 

 other equipment was pumped from the river." 



Bacterins and Their Use 



Typhoid fever has been largely brought under control by means of a 

 vaccine known as a haderin because it is made from dead causative 

 bacteria. The principle underlying vaccination is that the body 

 works up an active immunity by the introduction of large numbers of 

 dead typhoid germs. The presence of the dead bacilli stimulates 

 certain living cells in the body to make antibodies, thus causing the 

 body to acquire immunity. The immunity acquired probably does 

 not last more than two or three years, so that typhoid inoculation 

 should be given within this period if continued immunity is to be 

 expected. Bacterins are now used as protective agencies against 

 cholera and plague. During the World War a mixture of four vac- 

 cines (typhoid bacilli, paratyphoid bacilli A and B, and cholera 

 spirilla) was used successfully by Castellani in Serbia to control these 

 diseases. A vaccine made of living bovine bacilli cultivated in the 

 laboratory long enough to make them lose their virulence is the basis 

 of the Calmette vaccine which is used as a preventive against tuber- 

 culosis. There seems to be divided opinion as to the value of this 

 treatment. 



The Menace of the Carrier 



Although we can protect our milk and water supplies and to a very 

 large degree control typhoid through the use of cooked rather than 

 raw foods, we cannot protect ourselves adequately from the one 

 menace that keeps typhoid and certain other intestinal diseases con- 

 stantly with us. People recovering from typhoid frequently carry 

 bacteria in the body for some time after the disease. Such people are 

 called temporary carriers. Frequently the germs are carried for 

 longer periods, the person being apparently well. People have been 

 found to be carriers when no typhoid history can be traced. Such a 

 chronic carrier was the cook known as "Typhoid Mary." Presum- 

 ably the typhoid bacilli were transferred to food by means of her 

 dirty hands. During a period of fourteen years she was responsible 

 for forty-nine cases of typhoid. The typhoid carrier is more com- 

 mon than is usually realized, and since isolating carriers is a form 



