114 BACTERIOLOGY FOR NURSES 



Exotoxins. There is evidence that the exotoxins or true toxins 

 are of a protein nature, although nothing is known of their chemi- 

 cal structure; nor is it known whether they are secretory or 

 excretory products. They are, however, undoubtedly produced 

 by bacteria during their growth. They are poisonous in minute 

 doses ; reproduce characteristic symptoms and lesions of the disease 

 after a period of incubation ; are soluble in water ; are destroyed 

 by heat, and in the animal body stimulate the cells to produce 

 defensive substances which neutralize them, so-called antitoxins. 



The three well-known exogenous toxins are those produced 

 by B. diphtherise, B. tetani, and B. botulismus. They can be 

 produced apart from the body by growing the organisms on cul- 

 ture medium; the toxin passes from the bacterial cell and is 

 diffused throughout the substance on which the bacteria are grow- 

 ing. If broth is employed the toxin can be obtained germ free 

 by passing the broth through a porcelain filter. All attempts 

 to separate the toxin from the broth have failed. The only way 

 its presence can be recognized is through its effects on animals. 

 By this means it is possible not only to determine the presence of 

 the poison but also its strength. 



As already stated, true toxins are poisonous in exceedingly 

 small amounts. Tetanus toxins have been prepared from cultures 

 of the bacilli so strong that .0002 gram would be a fatal dose for 

 a man weighing 140 pounds. 



Another of the most distinguishing features of the true toxins 

 is their ability to produce all the characteristic symptoms that 

 arise when the disease is naturally contracted and the specific 

 organisms are present. Thus after an injection of diphtheria toxin 

 an animal will show depression, necrosis of the tissue at the site of 

 inoculation, post-diphtheria paralysis, etc. 



Small amounts of diphtheria or tetanus toxin prove fatal when 

 circulating in the blood stream ; larger quantities, however, when 

 taken by mouth are not injurious because they are immediately 

 destroyed by the digestive juices. On the other hand, the toxin 

 of botulism is absorbed by the mucous membranes of the intes- 

 tines and by this route gains entrance to the circulation. A strange 



