THE CONQUEST OF DISEASE 



things. Infective organisms may be intro- 

 duced into an animal, and then the battle be- 

 tween the parasites and the white blood cells 

 watched with the microscope. The toxic sub- 

 stances are extracted from the blood and 

 studied; the infective microorganisms are re- 

 moved and cultivated artificially; the toxins of 

 artificially grown organisms are introduced 

 into other animals, and the symptoms of the 

 disease reproduced; infected animals are in- 

 jected with artificially prepared toxins, and the 

 natural overwhelming of the infective agents 

 hastened; immunity is secured by introducing 

 the products of the bacteria into the healthy 

 animal and rendering the fluids and tissues of 

 the body obnoxious to their growth ; and steril- 

 ized products of the microorganisms are in- 

 jected to test the reaction of the animal to a 

 particular infection, thus determining whether 

 it is free from or suffering with a specific 

 disease. 



These are but a few of the animal experi- 

 ments which are employed in connection with 

 the infective diseases. Every one of these ex- 

 periments, having been worked out upon the 

 lower animals, has been applied to man with 

 results of such great importance that the period 



56 



