216 



FIRST YEAR SCIENCE 



taken that people who are susceptible to the disease shall 

 not be exposed to the germs. 



When disease bacteria get established in the system, 

 they secrete a poison called toxin, which is absorbed by 

 the blood and carried throughout the body, thus poisoning 

 many other parts beside those immediately attacked by 

 the bacteria. The cells of the body at once begin to se- 

 crete a substance to counteract this poison, an antitoxin. 

 If the vitality of the patient is great enough, sufficient anti- 

 toxin will be secreted to neutralize the effect of the toxin 

 and the disease will be overcome. 



Of late years it has been found that these antitoxins 

 can be artificially supplied or caused to develop. Thus 



the system may be aided in 

 neutralizing the effect of the 

 toxin, and in warding off the 

 disease. By injecting these 

 antitoxins or stimulating their 

 development, people are now 

 protected against smallpox, 

 diphtheria and other diseases. 

 Disease bacteria are not only 

 found in the air, but also in 

 water and milk and other kinds 

 of food. We must therefore 

 these germs from our water, 

 Many cases of tj-phoid fever 

 have been directly traced to the milk supplied by a 

 dealer in whose family was a case of the fever. Flies (Fig. 

 106) are great carriers of bacteria and, by crawling over 

 food, spread diseases. 



Germs thrive particularly in sewers, cesspools and un- 

 sanitary places, so that these should be especially watched. 

 The best guards against disease, however, are plenty of 



Fig. 106. 



be very careful to keep 

 milk and food supply. 



