408 



PLANTS AND MAN 



and should be barred from work in which they might pass their 

 disease bacteria to others. 



Milk, being an important human food, as well as an ideal 

 medium for the growth and multiplication of many bacteria, 

 must be adequately safeguarded. Many epidemics of septic sore 

 throat, typhoid fever, and other diseases have been laid to faulty 

 handling of milk. Proper dairy conditions and pasteurization of 

 milk will make this important food source safe. 



Water likewise is a great potential source of disease if not 

 properly safeguarded, since it often comes from rivers into which 



Fig. 250.— Tu- 

 berculosis bacilli 

 are slender rod- 

 shaped cells. 



Fig. 251.— Diph- 

 theria is caused 

 by a slightly curved 

 bacillus. 



sewage is emptied. The use of chlorine as a disinfectant for city 

 water supplies and the refinement of sewage disposal systems 

 have greatly lowered the death rates of typhoid fever. 



The three types of bacteria noted on page 404 all contain 

 disease producing members, but the latter are especially found 

 in the bacillus group which contains those species causing typhoid 

 fever, diphtheria, tuberculosis, dysentery, leprosy and tetanus. 

 Tuberculosis is one of man's most stubborn present day diseases, 

 caused by a slender rod shaped cell which gets into the body by 

 way of the respiratory or intestinal tracts (fig. 250). From here it 

 migrates to various parts of the body — the lungs being a favorite 

 place — and multiplies to form extensive colonies which cause a 



