696 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



the organism injected produces its diseased effects by endotoxins held 

 within the bacterial cell rather than by toxins. There is no evidence 

 indicating the presence of natural antiendotoxins in any animal. 

 The antibacterial action of the blood may be due to two constituents, 

 namely, cellular substances (leucocytes) and chemical substances in 

 the serum. The rat and the dog are both immune to anthrax but the 

 immunity of the dog is not due to antibacterial substances but to the 

 phagocytic activity of the leucocytes, while in the rat the immunity is 

 not due to the leucocytes but to the antibacterial substances. In 

 order to demonstrate the fact that the leucocytes are not responsible 

 for the immunity in the given animal it is necessary to combine the 

 bacteria in question with the leucocytes and serum in vitro and after 

 incubation make a careful examination with these cells to see if they 

 have taken up any bacteria. 



Antibacterial action is due to two substances in the serum: First, 

 the thermostable substance which combines with the bacteria called an 

 amboceptor; and second, a thermolabile substance called a complement, 

 which combines with the amboceptor after this substance has combined 

 with the bacterial cell. It is sufficient' to say at this time that these 

 substances occur in normal sera and that the result of their combination 

 with the bacterial cell causes the death of the bacteria and in some cases 

 a lysis (solution) of the bacteria in addition. 



There may be present in the blood of animals antibacterial sub- 

 stances of three kinds: First, those just killing bacteria (bactericidal); 

 second, those killing the bacteria and dissolving them (bacteriolytic) ; 

 and third, the leucocytes which are active in the ingestion of the specific 

 microorganisms and subsequently digest and destroy them. In all 

 probability the overactivity of leucocytes in every case of natural 

 phagocytic immunity is due to the presence of normal opsonins sub- 

 stances which sensitize the bacteria and render them susceptible to 

 phagocytosis. 



Normal Hemolysins. Normal hemolysins (hemoglobin-liberating 

 substances) are present in the sera of certain animals for the red blood 

 corpuscles of other animals of different species, and for the same species, 

 but never for the red corpuscles of the animal from which the serum was 

 obtained. Such substances known respectively as heterolysins and 

 isolysins and if the latter occurred the name autolysin would be applied. 



Normal Agglutinins. Normal agglutinins for various bacteria, such 



