262 BACTERIOLOGY 



terial toxins that have been modified by the vital action 

 of the integral cells of the body; and Roux^ and Buchner^ 

 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,^ Ehrlich/ 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 idioplasrri, 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- 



' Annales de I'lnstitut Pasteur, 1894, p. 722. 

 = Berliner klin. Wochenschritt, 1894, No. 4. 

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



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

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



