262 BACTERIOLOGY 



terial toxins that have been modified by the vital action 

 of the integral cells of the body; and Rpux 1 and Buchner 2 

 maintain that they exhibit their protective functions less 

 by direct combination with the toxins than by a specific 

 stimulation of the tissue-cells that enables the latter to 

 resist the harmful influences of the toxins. On the other 

 hand, Behring, 3 Ehrlich, 4 and their associates contend that 

 they are vital tissue elements, having the property of com- 

 bining directly with the toxins to form "physiologically 

 inert toxin-antitoxin" compounds that are in a manner 

 analogous to the double salts of familiar chemical reactions. 



Natural Immunity. It is well known that among man 

 and the lower animals individuals are frequently encountered 

 who are, in general, less susceptible to infection than are 

 others of their species; and that particular species of animals 

 not only do not suffer naturally from certain specific diseases, 

 but resist all efforts to produce the diseases in them by 

 artificial methods; in other words, they are naturally im- 

 mune from them. The term "natural immunity," as here 

 employed, implies a congenital condition of the individual 

 or species, a condition peculiar to his idioplasm, which has 

 been transmitted to him as a tissue-characteristic through 

 generations of progenitors. 



Acquired Immunity. Again, it is often observed that an 

 individual or an animal after having recovered from certain 

 forms of infection has thereby acquired protection from 

 subsequent attacks of like character; in other words, they 

 are said to have acquired immunity from this disease. " Ac- 



1 Annales de Tlnstitut Pasteur, 1894, p. 722. 



2 Berliner klin. Wochenschrift, 1894, No. 4. 



3 Infektion und Disinfektion, Leipzig, 1894, S. 248. 



4 Klinisches Jahrbuch, 1897, Bd. vi, Heft 2, S. 311. Fortschritte der 

 Medicin, 1897, Bd. xv, No. 2. 



