28 THE ETIOLOGY OF THE BACTERIAL DISEASES. 



In studying bacterial products it will be necessary for us to con- 

 sider the conditions under which they are formed. We will be com- 

 pelled to study those substances formed in artificial cultures as well 

 as those formed in the animal body. Indeed, in some instances we 

 will find our knowledge confined to investigations made under more 

 or less artificial conditions, and it will be well for us to remember 

 that caution must be exercised in drawing conclusions from knowl- 

 edge thus obtained. It might be well at this place to distinguish 

 between pathogenic and toxicogenic bacteria. A pathogenic bac- 

 terium is one which, as the name implies, induces a specific disease 

 which is recognized by more or less well-marked and characteristic 

 symptoms during life, or by more or less definite lesions found after 

 death, or by both. Pathogenic bacteria are always capable of growth 

 in the animal body, in which they multiply and elaborate their spe- 

 cific toxins. All pathogenic germs are toxicogenic, but it does not 

 follow that all toxicogenic bacteria are pathogenic. A toxicogenic 

 microorganism is one which, as this name also implies, is capable of 

 producing a poison or poisons. A toxicogenic germ may or may not 

 be capable of growth in the animal body. It may multiply in milk 

 or some other article of food before its introduction into the body, 

 and may in this menstruum elaborate more or less powerful poisons. 



In the second place we will proceed to give a brief historical 

 sketch of the discovery and study of the bacterial poisons; and, 

 thirdly, we will pass on to a discussion of the special products of the 

 specific pathogenic bacteria. In doing this we will not confine our- 

 selves to the chemistry of toxins but will extend our discussion to 

 their action on animals and the pathological changes induced by them. 

 After discussing the subjects mentioned above, we will proceed to 

 the study of those conditions of the animal body which influence the 

 growth and development of bacteria in the same. This will involve 

 a study of the germicidal constituents of the blood, the agglutinating 

 action of blood serum, the production and action of the toxins, the 

 production of immunity and the treatment of the infectious diseases 

 by serum therapy. 



On the conclusion of the above-mentioned studies we will investi- 

 gate questions pertaining to poisonous foods which owe their harm- 

 ful properties to the presence of toxicogenic bacteria. In this con- 

 nection we will present the known facts concerning food poisons and 

 the methods of their detection. 



