THE DEFENSES OF THE BODY 279 



So far as we can learn the blood serum exhibits normally 

 a small amount of antitoxic, agglutinative, and bactericidal 

 action against a great variety of pathogenic bacteria. The 

 nature of the agents responsible for these activities is believed 

 to be identical with that of similar agents found in the 

 blood of artificially immunized animals, though in the latter 

 instance they are always present to a higher degree than 

 in normal animals. 



To those ill-defined substances whose affinities are re- 

 stricted to the soluble toxins elaborated by the invading 

 bacteria the name "antitoxins" is now generally applied. 

 Contrary to what we have seen in the case of the germicidal 

 substances, normally present in the blood, antitoxins are 

 to be detected in the normal animal organism in very small 

 amounts. When they do exist under such conditions they 

 are of but comparatively feeble potency. 1 



In the great majority of instances antitoxic activities are 

 acquired peculiarities; acquired in some cases in a more or 

 less natural manner, as in the course of a non-fatal attack 

 of a specific malady; induced in others by purely artificial 

 means, as in the case of immunization from diphtheria 

 and tetanus. 



Our acquaintance with the antitoxins extends little beyond 

 their physiological functions and some of .the means that 

 induce their generation. We have no satisfactory knowledge 

 of their intimate nature or of the primary sources of their 

 production. They are believed by some (Buchner 2 and 

 Metchnikoff 3 ) to represent, when artifically induced, bac- 



1 See Bolton, Transactions of Association of American Physicians, 1896, 

 xi, 62. Pfeiffer, Deutsche med. Wochenschrift, 1896, No. 8. Fischl and 

 v. Wanschheim, Centralblatt fur Bakteriologie,' Parasitenkunde, und 

 Infektionskrankheiten, 1896, Abt. i, Bd. xix, S. 652. Wassermann, Berliner 

 klin. Wochenschrift, 1898, No. 1. 



2 Miinchener med. Wochenschrift, 1893, Nos. 24 and 25. 



3 Weil's Handbuch der Hygiene, Bd. ix, Lieferung 1, S. 48. 



