CONTROL OF DISEASE 339 



256. Immunity modifiable. ]\lany of the bacteria which cause 

 diseases are present in most of us a great part of the time; 

 yet we are not constantly getting sick. A good deal depends 

 upon the condition of the organism at a given time. Pasteur 

 performed an experiment which taught a very important lesson 

 regarding the modification of immunity by conditions. If the 

 bacteria of the cattle disease anthrax are injected into a hen, 

 the animal does not Seem to be affected one way or the other. 

 Pasteur placed a hen in a dish of cold water. until the animaFs 

 blood was lower than normal (104° F. for the hen). When 

 chilled in this way, the animal succumbs to anthrax. Anything 

 that influences the body unfavorably may thus increase the 

 susceptibility or overcome the resistance of the body. It is 

 therefore important to guard the natural immunity of the body 

 against the destructive effects of worry, of undue exposure to 

 extremes of temperature, of excessive fatigue or insufficient rest 

 and sleep, of improper nutrition, of prolonged hunger and thirst, 

 and of drugs, alcohol, or other substances that interfere with 

 the action of the blood as a living tissue. 



Disease itself may lower the resistance of the body. After 

 pneumonia, for example, one is more likely to catch other dis- 

 eases ; and he is more likely to catch pneumonia after t^^hoid 

 or measles than he is ordinarily. One cannot afford to be sick 

 even a little; even a slight cold may open the way for more 

 serious trouble. On the other hand, one who recovers from a 

 certain disease becomes almost wholly immune to that disease. 

 As the common saying goes, "You can't have measles twice." 

 The same is true of mumps, whooping cough, scarlet fever, 

 typhoid fever, and smallpox. How is this immunity brought 

 about ? 



257. Antitoxins. The venom of a rattlesnake, a certain pro- 

 tein found in the seed of the castor-oil plant, and many other 

 proteins act as poison in the body of another organism. When 

 one of these is brought into the blood of a human being, for ex- 

 ample, a chemical reaction is started in the living cells, espe- 

 cially the white corpuscles. As a result a new substance is 



