PROBLEM 2. How We Cm Conquer Some Diseases 



327 



Fig. 296 A stage in the preparation of typhus vaccine. Of what advaiitage is it to 

 use eggs instead of an aJiimal in the preparation of vaccine? (wide world) 



of the disease the germs pass out with the 

 excretions so that they are eventually 

 found wherever the sewage goes, in the 

 soil or in streams and lakes. In a later 

 problem you will discover how one case 

 of typhoid fever in a community might 

 sometimes start an epidemic. Immunity 

 can be given by inoculation with dead 

 t>'phoid germs. The dead bacteria stimu- 

 late the tissues to make antibodies. Be- 

 cause immunity lasts only a few years 

 the inoculation, or "vaccination" as it is 

 sometimes loosely called, must be re- 

 peated if one is to be continuously pro- 

 tected. Ever since the first World War, 

 everyone in the United States armed 

 forces has been immunized against ty- 



phoid. Civilians, too, are frequently im- 

 munized if there is any likelihood of 

 their being exposed to the germ. This has 

 very much decreased the number of cases. 

 Immunization against other diseases. 

 Measles, like rabies, is caused by a filter- 

 able virus. Doctors have now succeeded 

 in making a vaccine from measles virus 

 cultured on fertile hen's eggs. Many 

 children have already been made actively 

 immune to measles with this vaccine. x\c- 

 tive immunity can be given to children 

 against scarlet fever and whooping 

 cough, also. Even though these vaccines 

 do not always result in complete immu- 

 nity they at least protect the child from 

 a serious case of the disease. 



