260 MEDICAL BACTERIOLOGY 



dies or disintegrates and is then liberated. Solutions of this substance, obtained 

 by extracting dead bacteria with water or salt solution, when injected into 

 animals produces some or all of the pathological changes and obvious signs of 

 disease that are commonly produced by infection with the species of bacteria 

 from which the soluble extract was obtained this substance is referred to as 

 intracellular toxin or endotoxin. 



Endotoxins obtained from different species of bacteria differ in quantity, 

 quality and resistance to heat. They all withstand heating to 55C. for J^ 

 hour, many withstand exposures of several hours to 6oC., 7oC., 8oC. or even 

 90C.; a few. like tuberculin, withstand heating to noC. for several hours. 



Repeated ascending doses of endotoxin obtained from certain species of 

 bacteria confer immunity to the species from which the endotoxin was ob- 

 tained a specific immunity. 



There is a close similarity in many respects between aggressin and endotoxin, 

 in fact, Wassermann and Citron believe that what Bail described as aggressin 

 is in reality endotoxin. 



As a general rule, to which there are exceptions, the virulence of a bacterium 

 is proportional to the nocuous power of its endotoxin. 



Ectotoxin. A few of the pathogenic bacteria throughout their active life 

 emanate highly poisonous soluble substances that are absorbed by the tissue 

 or medium upon which the bacteria are located. This poisonous emanation is 

 referred to as extracellular toxin or ectotoxin. It is water-soluble and serum- 

 soluble. The pathogenicity and virulence of bacteria that produce ecto- 

 toxin are largely dependent upon and proportional to the nocuousness of the 

 emanation. 



The ectotoxins as a whole are much less resistant to heat than endotoxins, 

 the most stable being destroyed at iooC. in a few minutes. 



The ectotoxins produced by different species of bacteria differ widely in their 

 affinity for and effect upon tissue cells in vivo. 



Repeated injections of ectotoxin confer a relatively high degree of immunity 

 to the specific ectotoxin injected and a slight immunity to the species of bacteria 

 from whence it came. 



If we study different strains of a single species or successive generations of a 

 single strain, it soon becomes evident that bacteria vary in their toxin produc- 

 tion; this is especially true of ectotoxin production. Slight alterations in tem- 

 perature, aerobiosis, hydrogen ion concentration, acidity or alkalinity of 

 environment, and pabulum, cause sudden, marked increases and decreases in 

 ectotoxin production. 



At times, for no apparent reason, cultures cease producing ectotoxin, the 

 cessation being temporary or permanent. There are conspicuous exceptions as 

 in the case of the diphtheria bacillus cultivated by Williams which has remained 

 practically constant in its toxin production for years. 



VIRULENCE 

 The virulence of bacteria is subject to alteration by many factors, some of 



