SAFEGUARDS OF THE BODY AGAINST DISEASE 499 



bacillus is taken into the body, it is thought to go into the large 

 intestine, where it creates an acid medium. Some scientists think 

 this aids the work of the bacteria of putrefaction and, conse- 

 quently, clears up auto-intoxication. Recently another strain of 

 bacteria that sours milk has been found that seems to be more 

 effective. It is the Lactobacillus acidophilus. These bacteria will 

 live longer in the intestine than do the Lactobacillus bulgaricus. 

 There are a number of other conditions that protect the body 

 against the invasion of germs. Even after germs enter, very 

 few can cause a disease unless they multiply in great numbers. 

 The body may be thought of as a great living culture medium. 

 The inside is dark, moist, warm, and supplies food in the form of 

 digested foods or tissue cells for invading saprophytes or parasites. 

 In reality, each specific germ needs a definite combination of con- 

 ditions. For example, the temperature of the body is not high 

 enough for the bird type of tuberculosis. Therefore, this type 

 cannot attack man. The human type grows only between 

 37 C. and 40 to 41 C. A bird's temperature is much higher 

 than man's, so that human tuberculosis cannot grow in birds. 

 Bacteria that ordinarily attack warm-blooded animals are not 

 likely to affect cold-blooded ones. If, however, the temperature of 

 the cold-blooded animals is raised, they become susceptible to the 

 invading germs. Frogs are naturally immune to tetanus, but if 

 their temperature is raised, they become susceptible to the disease. 

 Bacteria such as tetanus are anaerobic and grow only in the 

 absence of air. If tetanus enters a surface wound exposed to 

 air, it does not multiply. It is only when it enters deep wounds, 

 where there is no air present, that it sets up an infection. Most 

 tissue cells offer a high natural resistance to the entrance of germs. 

 It is only when they are torn or lacerated that conditions are favor- 

 able for the growth of germs in them. Many bacteria taken in with 

 food are of the saprophytic type. They make no attempt to at- 

 tack the tissues but simply feed on food in the alimentary canal. 



