THE CHEMISTRY OF BACTERIA 47 



into iine threads. This capsule consists mainly of a protein, 

 mucin, similar to that found in the saliva. Sometimes, as in the 

 case of the iron bacteria, they are surrounded with a sheath in 

 which are large quantities of iron. Often such organisms are 

 found in water. When the water is first drawn from the well it 

 is normal in color, but, on standing, the iron in the sheath rusts 

 and is oxidized, and we have a yellow water. These organisms 

 are without significance from a sanitary viewpoint, but at times 

 they form in large masses and clog the pipes. The rather tough 

 bacterial wall consists of a compound, chitin, about midway be- 

 tween proteins and carbohydrates. 



The inner part of the cell is composed largely of bacterial 

 proteins which vary widely with different species of bacteria. 

 Many of them are highly poisonous. 



Toxins. — Poisonous protein substances may result from bac- 

 teria in two ways. First, the bacterial body may break down with 

 the formation of poisonous products. Second, the bacteria may 

 actually manufacture toxic products. To this second class of 

 poisons is given the name, toxins. Toxins have certain character- 

 istics which differentiate them from other poisons. 



1. Toxins are specific, that is, the diphtheria organism produces 

 a poison which if placed in the body of a susceptible animal will 

 give rise to diphtheria. We can grow the diphtheria bacteria in 

 beef tea and remove the bacteria; this beef tea will then cause the 

 disease, diphtheria. Diphtheria organisms alone produce diph- 

 theria toxin; the lockjaw organisms produce lockjaw, etc. Hence, 

 toxins are specific. 



2. Toxins are extremely violently poison, far surpassing any 

 other known poison in this respect. 



Smallest quantity of atropin required to kill man 130 mg- 



Smallest quantity of strychnin required to kill man .... 30-40 mg. 

 Smallest quantity of cobra venom required to kill man . . . 4.4 mg. 

 Smallest quantity of tetanus toxin required to kill man less than 0.23 mg. 



The tetanus toxin is produced by the germ which causes lockjaw. 

 The poison has never been obtained pure, yet the crude material 



