INFECTION AND INTOXICATION. 3 



which we so often read, of epidemics occurring suddenly to 

 large numbers of persons from the ingestion of partly decom- 

 posed meat, fish, sausage, milk, etc. Infection is therefore to be 

 distinguished from intoxication, inasmuch as the first presup- 

 poses the existence of a living agent which enters the body 

 and survives there, while the second is to be attributed to the 

 effects of any toxic agent which may be present in the body in 

 sufficient amount to produce more or less marked symptoms of 

 disease. The relation of intoxication to infection cannot be 

 better expressed than in the following paragraph. " It is im- 

 possible to draw any sharp dividing line between intoxication 

 and infection ; but it is believed to conduce to precision and 

 clearness to regard as agents of infection only such as are 

 capable of reproduction, that is, such as are living organisms 

 and not include among these agents chemical poisons whether 

 produced by bacteria or other vegetable cells or by animal 

 cells" (Welch). 



There is perhaps a tendency at the present time to minimize 

 the importance of the living agents themselves in the produc- 

 tion of the phenomena of infectious disease, and to ascribe 

 these entirely to the action of the toxic agents manufactured 

 by the micro-organisms. But in view of the fact that in several 

 typical infectious diseases, among which may be mentioned an- 

 thrax, asiatic cholera, and typhoid fever, it has been found quite 

 impossible to separate in an active form the toxic products 

 from the bacteria which produce them, the latter cannot be 

 regarded as less essential to the production of the disease than 

 the former. Indeed there are few diseases at present known 

 in which all the symptoms can be ascribed to the toxic products 

 of the micro-organisms alone. To quote another paragraph from 

 Dr. Welch's writings : " In the case of most infectious dis- 

 eases we can no more separate the actual presence, multiplica- 

 tion, and specific vital activities of the bacteria within the body 

 from the disease than we can substitute any chemical substance 

 for the actual presence and growth of the yeast fungi in the 

 production of alcohol from sugar." 



Yet the role played by the chemical substances developed 

 from certain bacteria in the production of the phenomena of 



