52 GENERAL PHYSIOLOGY OF BACTERIA 



them. Vaughan 1 has studied both enzymes and toxins extensively, 

 and has summarized admirably the points of resemblance between 

 exo-enzymes and exo-toxins as follows: 



"1. Both are destroyed by heat. 2 



"2. They act in very dilute solution. 



"3. When repeatedly injected into animals in non-fatal doses they 

 cause the body cells to elaborate antibodies which neutralize the toxin 

 (or the enzyme) both in vivo and in vitro. 



"4. In the development of their effects a period of incubation is 

 required. 



"5. It has been shown (by Abderhalden) by optical methods that 

 they have a cleavage effect upon proteins they split complex proteins 

 into simpler bodies; in other words, they have a proteolytic action. 



"6. They are specific in two senses: (a) they are specific according 

 to the cell which produces them; (b) they are specific in the antibody 

 elaborated in the animal body after repeated injections of non-fatal 

 doses." 



Bacterial toxins are usually classified as exo- or soluble (extra- 

 cellular) toxins, and endo- (intracellular) toxins. The former are 

 soluble and diffuse out from the bacterial cell into the surrounding 

 medium. Very few bacteria produce exo-toxins: the best known are 

 those of the diphtheria, tetanus, and botulismus bacilli. To these 

 specific antitoxins are known. Endo-toxins are non-diffusible and are 

 locked up in the bacterial cell; they are liberated only when the 

 cell disintegrates. No specific antitoxin has been produced for an 

 endo-toxin. 



Ptomains. Ptomains are soluble, basic, nitrogen-containing sub- 

 stances formed from proteins or protein derivatives by the action of 

 microorganisms. They are non-specific, relatively poor in oxygen 

 content, and probably simpler in composition than either exo- or endo- 

 toxins. No antibodies have been produced against them. Some are 

 poisonous, many are not. 



L. PIGMENTS. 



With the exception of bacteriopurpurin, which occurs in the sulphur 

 bacteria and is supposed to be photodynamic and, therefore, somewhat 

 analogous to the chlorophyll of the higher plants, the significance of 



1 Protein Split Products, Lea & Febiger, Philadelphia and New York, 1913. 



2 Although they are somewhat more resistant to heat than the cells which produce 

 them. 



