676 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



, SoLXJBLE Toxins. — It is a known fact that there are some patho- 

 genic bacteria which secrete through their cell walls poisons which 

 diffuse into the surrounding media. Tp these poisons or toxins the 

 disease symptoms are due. Bad. diphtheria of diphtheria, B. tetani 

 of lock-jaw or tetanus, Bact. dysenteria of bacillary dysentery, B. 

 potuUnus of meat poisoning, and Ps. pyocyanea, the causal organism of 

 blue-green pus, are about the only bacteria of this character. Some 

 bacteria, such as Strepi. pyogenes and M: pyogenes -oar. aureus produce 

 hemolytic toxins. There are certain protozoa as, for example, cer- 

 tain entamcebae and the va,rious trypanosomes which secrete soluble 

 poisons. Among the animals, the venoms of the poisonous snakes, the 

 poison of -the centipedes and spiders, the serum of the eel, and the 

 excretion of the dermal glands of the toad are examples of secreted 

 toxins (zootoxins). Again, among the plants are abrin from the 

 jequerity bean, ricin from the castor oil bean, and others, are examples 

 of soluble toxins the product of plant cells (phytotoxins). The cells 

 producing these toxic substances, therefore, are only indirectly re- 

 sponsible for the infections for it is the toxins themselves which produce 

 the pathogenic effect on the body. 



Endotoxins. — Many of the pathogenic bacteria and some of the 

 protozoa do not secrete their toxins outside the cell wall but hold 

 them within the wall in combination with the protoplasm. They do 

 not liberate these substances until the microorganisms die and are 

 disintegrated. Such toxic substances are called endotoxins to dis- 

 tinguish them from those secreted from the cell, namely, the soluble 

 toxins. Two of the best examples of pathogenic bacteria , of this 

 type are the Msp. comma of Asiatic cholera and B. typhosus of 

 typhoid fever. 



Toxic Bacterial Proteins. — ^There are some bacteria and other 

 parasitic cells which produce a small amount of endotoxin and in 

 certain instances some soluble toxin but not enough of either of these 

 substances to account for the toxicity of the organism. It has been 

 found that when organisms of this character are ground up and washed 

 to free them of their endotoxin and are washed free of all soluble 

 toxins, they are still toxic. It has been shown that this toxicity is due 

 to the protein substances of the cell. The Bact. tuberculosis aad. the 

 Bact. mallei of glanders are two notable examples of microorganisms 

 of this character. When, for example, the proteins of Bact, tuberculosis, 



