572 BACTERIOLOGY. 



between the invading organisms on the one side and 

 the resisting tissues of the animal body on the other ; 

 the weapons of offence of the former being the poison- 

 ous products of their growth, while the means of 

 defence possessed by the latter are the phagocytic cells, 

 such as the leucocytes, the large mononuclear cells of 

 the blood, and the connective tissue and endothelial cells, 

 as well as the vital substances which act, so to speak, as 

 antidotes to bacterial poisons. If the leucocytes and 

 tissue elements are not of sufficient vigor to destroy the 

 invading bacteria or to render inert the poisons pro- 

 duced by them, the bacteria are victorious and infection, 

 in different degrees of severity, results ; on the other 

 hand, if there be failure to excite disease, the tissues are 

 victorious, and are then said to be resistant to or immune 

 from this particular type of infection. 



In some cases the protective bodies possessed by the 

 animal act directly upon the invading organisms them- 

 selves i. e.j they are germicidal ; in others their func- 

 tion is more that of antidotes, or neutralizers in the 

 chemical sense, of the poisons produced by these organ- 

 isms, the organisms themselves, in certain instances, 

 experiencing only slight injury from a limited sojourn 

 in the living tissues. For those constituents of the 

 animal body that are by nature endowed with germi- 

 cidal peculiarities, the designations "alexins" (Buchner) 

 and "defensive proteids" (Hankin) have been sug- 

 gested. Careful investigation has shown that the normal 

 bactericidal properties of the blood serum rest upon the 

 presence of immune substances similar in nature to those 

 found in the blood serum of immune animals i. e., (I) a 

 specific immune body (intermediary body) for a partic- 

 ular organism, and (2) complement. So far as we can 



