TOXINS 173 



(2) many protozoa ; and (3) a few metazoa, generally 

 worms. The non-infective parasites are the animal 

 parasites generally, particularly many worms and 

 arthropods. 



The production of the phenomena of disease by patho- 

 genic organisms has in the past been ascribed to various 

 factors, such as the using up of the oxygen which should 

 go to the tissues, or of the proteins of the body and of the 

 food, or to the effects of plugging of the vessels by the 

 microbes. These are now considered to be subsidiary, 

 embolism and thrombosis being perhaps the most impor- 

 tant. We now regard the disease -complex as being 

 caused in the main by poisonous substances or " toxins " 

 formed by the infecting organisms. These toxins are 

 substances of a very complex composition, probably 

 allied to the proteins ; in some instances they seem to 

 be closely akin to enzymes or ferments, and they are 

 direct products of the bacterial cells. The toxins of most 

 pathogenic organisms, e.g. typhoid, cholera, plague, etc., 

 are more or less integral parts of the bacterial cells ; they 

 are " endotoxins," and are not excreted to any extent 

 into the culture medium, but may gain access to it 

 by autolysis of the organisms. In the body, endotoxins 

 may be set free by autolysis or some other mechanism. 

 A few organisms, notably Bacillus diphtherice and B. tetani, 

 produce extra-cellular toxins which are found in the cul- 

 ture liquid. The toxins are classified by Sidney Martin 1 

 as follows : 



( 1 ) Poisons produced by the digestive or the destructive 

 action of bacteria on proteins in the culture medium. 

 Examples of these are the poisons of the Bacillus anthracis 

 and of the pus-producing staphylococci. 



(2) Poisons which are the result of the digestive or 

 destructive action of bacteria on proteins, but formed as 



1 Manual of General Pathology, p. 76. 



