458 BACTERIOLOGY. 



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,^ as they are 

 collectively 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 diphtheria and of tetanus when under both 

 artificial cultivation and in the animal body. Many 

 bacteria which do not possess the power of generating 

 or secreting such poisons may, nevertheless, have inti- 

 mately associated with their protoplasmic bodies poison- 

 ous substances that can only be isolated by particular 

 methods; thus the toxins of bacillus tuberculosis and 

 of spirillum cholerce Asiaiicce are much more conspicu- 

 ously present in the protoplasm of these bacteria than 

 in the fluids in which they have grown, and Buchner 

 has isolated from several species of bacteria " bacterio- 

 proteins" having the common properties of solubility in 

 alkalies, resistance to the boiling temperature, attraction 

 of leucocytes (positive chemotaxis), and pyogenic 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-albumins, peptones, albumoses, and enzymes 

 or ferments. 



' " Toxius " Is tbe term commonly used to designate amorphous poisons of 

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

 poisons that are crystaZHzaUe. 



