88 THE BACTERICIDAL SUBSTANCES OF THE BLOOD 



substances, when infection in the untreated animal may be brought 

 about with subminimal infecting doses (as compared with a con- 

 trol animal), while in one that has been previously rendered hyper- 

 leukocytic this effect is not obtained. 



Upon the basis of analytical studies such as those outlined in 

 the foregoing pages, incomplete as they are, we can now distinguish 

 three different types of infection (excluding those with the so-called 

 necroparasites, in which a successful infection can scarcely be 

 brought about under ordinary conditions). In the first, represented 

 by the anthrax bacillus, the serum in itself is either inactive or 

 shows but slight inhibitory qualities, while the combination of 

 serum with leukocytes has strong antibacterial properties which 

 can be completely overcome, however, through the aggressivity of 

 the organism. 



The second type is represented by various streptococci, staphylo- 

 cocci and certain vibrios (el Tor.), i. e., organisms which stand very 

 close to the group of the true parasites. In such infections the 

 serum alone manifests but little bactericidal effect, while the anti- 

 bacterial action of the serum, when combined with leukocytes, 

 is strongly marked and can be only partially overcome by the 

 aggressivity of the organism. 



In the third type the serum alone, as well as in combination with 

 leukocytes, shows marked antibacterial properties, the former by 

 itself being sometimes sufficient to offset the aggressivity of the 

 corresponding bacteria. The animalization of the organisms is here 

 of little avail, as a protective measure against phagocytosis, while 

 it is partially effective in the case of the serum. Most members 

 of the typhoid and the vibrio group fall under this category. 



