BACTERIA 25 



portant that diphtheria be recognized and treated at the 

 earliest possible moment. The use of this antitoxin has 

 greatly reduced the proportion of deaths from diphtheria. 

 For instance, in New York the average annual death rate 

 from diphtheria fell from 15.19 in each 10,000 of the popu- 

 lation before the introduction of antitoxin to 6.62 in 10,000 

 after its introduction ; and in Vienna it fell from 8.14 to 2.95 

 in 10,000. If a person recovers from an attack of diphtheria, 

 he will not as a rule have the disease again, no matter how 

 often he may be exposed ; he is immune. Exceptions to this 

 rule, however, occur. Similar immunity is known in the 

 case of many other diseases, such as measles, smallpox, and 

 yellow fever. 



38. Typhoid Fever. This is due to a bacillus which 

 seems to be taken in only with food or drink (Fig. 9, C). The 

 bacillus lives and multiplies chiefly in the small intestine, 

 but also in other parts of the body, as the blood and the 

 marrow of the bones. As in the case of the diphtheria bac- 

 terium, its evil effects are due to a toxin which is absorbed by 

 the blood. This toxin, however, is not given off by the living 

 typhoid bacilli, but is a part of their living matter, and it 

 passes into the blood of the human victim only after the 

 bacilli have died. The most common source of typhoid in- 

 fection is impure water, and the purity of the water supply of 

 a city can be quite accurately judged by the number of cases 

 of typhoid in that city. Flies, which breed and seek their 

 food in filthy places, carry the typhoid germs about upon 

 their bodies and deposit them in milk, cream, or other food 

 that they touch. Flies carry many other germs besides that 

 of typhoid, and they are now well recognized as dangerous 

 distributors of disease. 



Persons who have been cured of typhoid fever may still 

 carry large numbers of actively multiplying typhoid bacteria 

 in their intestines or bile ducts ; this condition often lasts for 

 several months, and in some cases for years. Such carriers, 



