CONTROL OF DISEASE 



345 



saving a life and delaying proper treatment until it is too late. 

 A knowledge of the way the blood reacts to various kinds of 

 parasites has made it possible to make quick diagnosis in some 

 cases ; a knowledge of chemical changes produced in the body 



86 

 80 i 



70- 



60 



60 



40- 



30- 



20- 



10- 



JLE- 



1 



1 



1 



I 



I I 



! I 

 ill 



h Vi M 



'18 



1900 '01 '02 '03 '04 '05 '06 '07 '08 '09 '10 '11 '12 '13 '14 '15 '16 '17 



Fig. 163. Vaccination and typhoid fever 



The solid lines represent the United States army deaths from typhoid fever, per 

 100,000; the dotted lines the corresponding numbers for the civilian population. In 

 1909 vaccination against typhoid was made optional in the army; there was an im- 

 mediate improvement of conditions. In 19 11 vaccination became compulsory in the 

 army. Although there has been a steady improvement for the whole population, the 

 contrast between the vaccinated army and the generally not-vaccinated civilian 



population is very striking 



by some parasites helps in other cases, and in still other cases 

 it is possible to examine the bacteria directly. Swabs of cot- 

 ton that have been sterilized may remove from the throat colo- 

 nies of diphtheria bacilli, or the sputum (saliva) may contain 

 the bacilli of tuberculosis. These can be examined under the 

 microscope. 



The Widal test for typhoid has already been mentioned (see 

 Fig. 161). A test for susceptibility to diphtheria, devised by 



