INFECTION AND IMMUNITY. 41 9 



which certain of these organisms have been artificially 

 cultivated, substances which, when separated from the 

 bacteria by which they were produced, possess the power 

 of causing in animals all the constitutional symptoms 

 and pathological tissue changes that are seen to occur in 

 the course of infection by the organisms themselves. 

 In some instances these poisons, toxins 1 as they are col- 

 lectively called, appear to be the direct result of metabolic 

 changes brought about by bacteria in the medium or 

 tissues in which they may be developing, i. e., they are 

 products of nutrition that pass readily into solution, as 

 is conspicuously seen in the case of the bacillus of diph- 

 theria and of tetanus when under both artificial cultiva- 

 tion and in the animal body. Many bacteria which do 

 not possess the power of generating or secreting such 

 poisons may, nevertheless, have intimately associated 

 with their protoplasmic bodies poisonous substances that 

 can only be isolated by particular methods ; thus Buch- 

 ner has isolated from several species of bacteria u bac- 

 terio-proteius " having the common properties of solu- 

 bility in alkalies, resistance to the boiling temperature, 

 attraction of leucocytes (positive chemotaxis), and pyo- 

 genic powers. 



There is as yet little agreement of opinion as to the 

 chemical nature of toxins, but it is probable that the 

 group comprises different bodies of the nature of globu- 

 lins, nucleo-alburnins, peptones, albumoses, and enzymes 

 or ferments. 



Toxic ptomaines are probably not conspicuously con- 

 cerned in producing the characteristic symptoms of 



1 " Toxins " is the term commonly used to designate amorphous poisons of 

 a proteid nature ; while " ptomaines" is the term used to signify nitrogenous 

 poisons that are crystattizable. 



