BACTERIA AND DISEASE 407 



munity itself is given in the form of an antitoxin developed in 

 the body of another animal as described above. Diseases treated 

 in this way include diphtheria, tetanus, scarlet fever, measles, 

 and infantile paralysis. 



In addition to the immunity methods described above as 

 being valuable in preventing disease producing organisms from 

 causing illness, there are many public health practices which are 

 of enormous value in checking the spread of disease bacteria. 

 It is necessary for such organisms to travel from one host to 

 another, since conditions for their growth in one place never 

 remain favorable over long periods of time. Either their host 

 dies, the body rebels against them, or their own waste materials 

 begin to poison them. Therefore, if their pathway from one host 

 to another can be blocked, their spread and harm will be 

 checked. Such organisms often live in or upon some host other 

 than man and by eliminating these secondary hosts, the spread 

 of a particular disease can be checked. An example of this is seen 

 in the case of bubonic plague, which is primarily a disease of 

 rats and is transmitted by the bite of a flea. In times of severe 

 plague among rats, the fleas take to biting humans, inflicting 

 the plague upon them. Thus by controlling rats, the plague is 

 kept under control. 



Sanitation and general cleanliness are important in public 

 health work, since many disease organisms are present in human 

 excreta, and improper disposal of such refuse is likely to result 

 in contamination of man's food supplies. With bacteria as 

 passengers on dust particles in the air, it is wise to employ 

 soap and water frequently, as soap is a good mild antiseptic, 

 and the removal of excess moisture, oils arid dust from the 

 surface of the body by cleansing is one way of eliminating 

 bacteria. 



Many disease bacteria depend upon actual contact for trans- 

 mission from one host to another, consequently isolation or 

 quarantine of one known to be suflering from the disease is of 

 great importance in safeguarding the health and lives of others. 

 Unfortunately, some few people harbor disease producing organ- 

 isms in their bodies without themselves showing any signs of the 

 disease. Such individuals are known as "carriers" of the disease 



