BIOLOGICAL THERAPEUTICS. 

 By a. Eichhorn*. 



INTRODUCTION. 



The fundamental principles underlying biological therapy are inti- 

 mately connected with the study of immunity. In order to intelligently 

 apply biologic therapeutics to the treatment and prevention of disease, 

 it is essential to be familiar with the principles of immunity. It is true 

 that our knowledge of this intricate subject has not yet been made suffi- 

 ciently clear in all of its phases, nevertheless, the principles of the phe- 

 nomena are clearly understood. No doubt the extensive investigations 

 which are being carried out at present in this line will sooner or later 

 disclose a most wonderful activity which is taking place in the body dur- 

 ing the struggle between infection and resistance. The principal bio- 

 logic tests which have played such an important part in immunology will 

 be further advanced. Reference is made especially to the complement- 

 fixation, agglutination, precipitation, and other tests, and particularly to 

 the latest of them all — ^the Abderhalden test — which has conclusively 

 shown that not only in disease, but also under certain physiological con- 

 ditions, certain ferments, enzymes, or other products are developed by 

 the body and may be detected by the application of this test. It is there- 

 fore of the greatest importance that the subject of immunity should be 

 well understood by all those who apply biologic products to the treatment 

 and prevention of disease. 



Immunity. 



The study of immunity during the last few years has advanced to 

 such an extent that, not only has our theoretical knowledge of the subject 

 been furthered, but its practical usefulness has been established beyond 

 a doubt. The progress in this line has not been confined to the applica- 

 tion of the present knowledge of immunity to the science of human medi- 

 cine, but many of the reactions are now utilized in veterinary medicine. 



Immunity represents the resistance or non-susceptibility to disease, 

 or in other words the ability of the living organism (human or animal) 

 to resist the action of the causes of disease. Immunity is either natural 

 or acquired. The acquired immunity is again subdivided into active and 

 passive immunity. 



In glancing over the list of diseases to which various species of ani- 

 mals are susceptible it becomes evident that some animals are never spon- 

 taneously infected with many of the microorganisms that cause extensive 

 and fatal ravages in others. Such differences point to variations in the 

 defensive mechanism since" the invader in these cases is the same. This 

 non-susceptibility which is congenital or the result of normal growth is 

 called "natural immunity." 



Even in susceptible species infectious diseases frequently terminate 

 in recovery and recovered individuals are to a greater or less extent re- 

 sistant to future attacks of the same diseases. This condition is called 

 "acquired immunity." Acquired immunity may be brought about (1) by 

 inoculation with attenuated .virus, as for instance in vaccination against 



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