174 A MANUAL OF BACTERIOLOGY 



an excretion (the toxin) of the bacterium. The Bacillus 

 diphtherice is the best example of this. A similar com- 

 bination of poisons is found in snake-venom. 



(3) Poisons which are excretions only, such as those 

 produced by the tetanus bacillus. 



(4) Poisons which are typically intra-cellular, but 

 which may also be excretory. The poisons produced 

 by the typhoid bacillus, the Bacillus coli, the Bacillus 

 enteritidis of Gaertner, and the cholera vibrio belong to 

 this group. 



Thiele and Embleton 1 suggest that the toxins of most 

 bacteria are really cleavage products derived from their 

 cellular proteins under the influence of ferments present 

 in the body of the host. These cleavage products are, 

 however, toxic only at a certain stage of their disintegra- 

 tion. Given the power of existing and multiplying in 

 the body of the host, the pathogenicity of a bacterium 

 depends on the quantity and consequent activity of the 

 ferments of the host. A certain degree of ferment 

 activity renders the cleavage products of the bacterio- 

 protein toxic, a further degree of ferment activity carries 

 the disintegration so far that the cleavage products are 

 no longer toxic. A bacterium may therefore be harmless 

 to a host if the latter (a) has no ferments capable of 

 digesting its bacterio-protein ; (6) has such a poor supply 

 of ferments that the bacterio-protein is so slowly dis- 

 integrated that toxic products never attain a sufficient 

 concentration to be harmful ; (c) has such a plentiful 

 supply of ferments that the cleavage of the bacterio-pro- 

 tein rapidly passes beyond the toxic stage. A harmless 

 bacterium, e.g. B. megaterium, may be rendered patho- 

 genic if suitable ferments can be produced in the host 

 to bring about the necessary disintegration of its bacterio- 

 protein. 



1 Lancet, vol. i, 1913.. pp. 234 and 332. 



