122 INFECTION 



produce and contain toxic substances. When, owing to the peculiar 

 structure of the bacterial protoplasm or nature of the toxic substance 

 itself, the toxin can diffuse readily into a surrounding medium, the toxic 

 substance is known as a true, soluble, or extracellular toxin; when the 

 toxin enters into combination with the bacterial protoplasm, it becomes 

 known as an endotoxin. This union of toxin and bacterial protoplasm 

 may be so firm as to render the toxic substance inseparable from the 

 bacterial protein. The various toxic substances or toxins differ, there- 

 fore, according to their diffusibility through the membrane of bacterial 

 protoplasm, or their power of combining with these protein substances, 

 or both factors may be operative. 



Satisfactory antitoxins for endotoxins have not been produced, and this 

 is an important point in differentiating between a true toxin or an endotoxin 

 of any particular microorganism. Animals immunized against endotoxin 

 develop substances in their serum that are bactericidal, bacteriotropic, 

 and agglutinative to the bacteria from which the poisons were derived, 

 but the serum itself is not antitoxic for the endotoxins. Therapeutic 

 serums for use against infections caused by the endotoxin class of 

 bacteria are largely bacteriolytic and bacteriotropic in action. The 

 endotoxins of some bacteria, and particularly those of streptococci, 

 seem to repel the leukocytes, or exert a negative chemotactic influence, 

 which may effectually retard or entirely prevent phagocytosis; in this 

 respect they resemble the aggressins of Bail. Immune serums owe a 

 portion, at least, of their therapeutic value to the power they possess of 

 overcoming this influence and facilitating phagocytosis. These serums, 

 however, have not proved of as much value as have the diphtheria and 

 tetanus antitoxins in the treatment of the respective infections men- 

 tioned, and have proved a check to the progress of serum therapy. It 

 is probable that the endotoxins are more specific for the various strains 

 of the same species than are the true toxins, as indicated by the results 

 of Cole in the treatment of pneumonia with an anti-pneumococcus 

 serum corresponding to the type of microorganism responsible for the 

 individual infection, as determined by a rapid method of diagnosis 

 previous to the administration of serum. 



AGGRESSINS 



In an attempt to explain certain observations of Koch to the effect 

 that when a tuberculous animal is injected intraperitoneally with a fresh 

 culture of tubercle bacilli it succumbs quickly to an acute attack of the 



