THE CONQUEST OF DISEASE 



eases do so chiefly because their excretions are 

 poisonous to man. Their excretions produce 

 toxins, and have the power when absorbed into 

 the blood to cause the fever and other symp- 

 toms characteristic of the infectious diseases. 

 The parasites are destroyed in the body by 

 the white blood cells; and their destruction 

 is hastened by their being overcome by certain 

 other substances which are produced in the 

 body as a result of the stimulation by the toxins 

 themselves. This warfare between the bacteria 

 and their products, on the one hand, and the 

 leucocytes and body fluids, on the other hand, 

 constitutes disease. 



The symptoms of infective diseases repre- 

 sent the effort on the part of the body to rid 

 itself of certain foreign substances. The 

 natural tendency of these diseases is towards 

 recovery. So long as the foreign microorgan- 

 isms are present the white blood cells treat 

 them as foreign bodies and operate for their 

 destruction or elimination. Inflammation is 

 the life-saving process, showing the effort of 

 the body to limit their spread and summon its 

 resistance to overcome them. Finally, the 

 very presence of the toxins of the parasites 

 themselves helps to render the body uninhabit- 



