BACTERIAL PRODUCTS 19 



increased during the process of immunisation. Advantage 

 has been taken of the fact of this difference of stability 

 between these two substances to analyse the action of both 

 bodies. For example, if the blood serum of an animal 

 immunised against the red blood corpuscles of another 

 animal be mixed with a suspension of these same red 

 blood corpuscles in normal saline solution, it will be found 

 that, owing to the combination of this serum with the red 

 blood corpuscles, they are broken down, and the haemo- 

 globin is set free into the serum. 



If, now, the serum of the immune animal be heated to 

 55 C. for half an hour, and then be added to the red blood 

 corpuscles, they are not dissolved, and no haemoglobin is 

 liberated. If, however, a few drops of fresh serum be added, 

 the breaking down takes place immediately. The heated 

 serum contains the immune body, but the complement has 

 been destroyed. Along with the fresh serum, however, 

 complement is added, and the immune body, linking the 

 complement on to the substance of the red corpuscle, brings 

 about the breaking down of the corpuscle. Without the 

 complement, which is the real attacking body, the corpuscle 

 remains intact, just as it does when there is no immune 

 body by w r hich the attacking complement may be linked 

 on or brought into direct relation with the corpuscle. 



In relation to the prevention and cure of the diseases 

 depending upon bacteria, it must be noted that these patho- 

 genic organisms have their activity retarded or destroyed by 

 exposure to high temperatures, by the action of chemical 

 solutions, by being reproduced for several generations in the 

 bodies of certain animals, and in other ways. Antkrax virus 

 is thus attenuated by heat ; rabies virus by being grown in 

 the bodies of rabbits. These attenuated viruses are used as 

 protective vaccines. The vaccines of anthrax and rabies, as 

 well as those of black- quarter, swine erysipelas, and fowl 

 cholera, when injected into the bodies of animals liable to 

 these disorders, render the vaccinated subjects immune. 

 This is demonstrated by the animals operated upon suffering 

 no harm when subsequently inoculated with doses of the 

 unattenuated bacterium or its products, which would 

 destroy unprotected animals. 



