36 HUMAN BIOLOGY 



32. Prevention of diphtheria. — We have learned some- 

 thing of the means by which we can combat this disease 

 when once it has begun its attack. Antitoxin may also be 

 administered to any members of the family who have been 

 exposed to diphtheria, and it then becomes a means of pre- 

 venting the disease. But it is much more important, as is 

 the case with tuberculosis, to prevent all danger from attacks 

 by this disease than it is to know how to cure it. Here again 



we find strong arguments for the enforce- 

 ment of the rules against spitting, for liv- 

 ing bacteria are often found in the throats 

 of sufferers from what are thought to be 

 ordinary sore throats. For this reason, 

 Fig. 16. -Typhoid ^^ children should be especially careful 



bacteria. ' _ _ _ ^ •' 



to avoid putting into their mouths pencils, 

 coins, candies, or other objects that have been used by other 

 pupils, for diphtheria germs have been frequently transmitted 

 in this manner. 



33. Cause of typhoid fever. — Typhoid fever is a disease 

 caused by the growth in the tissues of the intestines of rod- 

 shaped bacteria. The typhoid bacteria have several hair- 

 Uke projections something like long cilia (known as flagella), 

 which vibrate rapidly and so enable the germs to move about 

 (Fig. 16). These bacteria are practically always taken into 

 the body through the mouth and thence into the intestines. 

 " Food and drink are usually the vehicles which serve for 

 the entrance of the bacillus, water and milk being probably 

 the most frequent sources of infection. The latter is es- 

 pecially dangerous from the fact that the typhoid bacillus 

 not only lives but multiplies in it. Water and milk, however, 

 are only dangerous when they actually contain the typhoid 

 bacilli which have entered into them from the excretions of 



