90 ELEMENTS OF GENERAL SCIENCE 



100. Transmission of typhoid bacteria. Within the body of 

 a person who has typhoid the number of bacteria may become 

 enormous and they may produce such injury as to cause death. 

 But no matter how many typhoid bacteria there may be that 

 affect this person, no other person would catch typhoid from 

 him unless some of the bacteria were transmitted to the second 

 person. Obviously it is of great importance that these disease- 

 producing bacteria shall not be transmitted from one person 

 to another. The way to prevent transmission of disease bac- 

 teria is to make sure that all bacteria from a person who has 

 typhoid or other disease are promptly killed. This is most 

 difficult, for it is not easy to sterilize everything that might 

 carry bacteria. Furthermore, some people who have recovered 

 from typhoid continue to have living typhoid bacteria in their 

 bodies for several years, thus making possible continuous 

 distribution of disease germs. 



101. Importance of pure milk and water. Milk and water 

 have often been the means of carrying typhoid bacteria. Many 

 cases show conclusively that when a dairyman or some mem- 

 ber of his family has typhoid, many of the people whose milk 

 supply comes partly or wholly from this dairy may take the 

 disease. Lack of care has made possible the introduction of 

 typhoid germs into the milk, and it is distributed to unsuspect- 

 ing patrons. 



If the water and milk are not polluted with typhoid, or 

 if, when polluted, they are sterilized, they do not carry the 

 disease. Milk may be pasteurized (that is, heated for twenty 

 minutes to between 140 and 150 F.), and this kills the ty- 

 phoid germs. The number of bacteria in a cubic centimeter of 

 milk or water may be very large. There may also be wide 

 variations in the number of these bacteria, due to different 

 ways in which milk and water are handled or to the length of 

 time they have been allowed to stand in places favorable to 

 the growth of the bacteria (fig. 48). Thus, in the city of 

 St. Paul, Minnesota, in a special investigation it was found 



