RELATION TO INFECTIOUS DISEASES. 91 



an important part in the production of morphological 

 changes, the nature of which will be indicated when these 

 diseases are discussed. 



(o) The germ may produce chemical poisons by splitting 

 up preexisting complex compounds in the body. This 

 theory finds, in the first place, strong support in the well- 

 known fact that many of the putrefactive germs produce 

 highly poisonous bodies ; and, in the second place, the for- 

 mation of chemical poisons will account for the appearance 

 of the symptoms of the disease when the microorganisms 

 never find their way into the blood. The correctness of 

 this theory has been tested by a large number of investi- 

 gators, and with the result that its truth has been firmly 

 established. It was soon found that pathogenic germs 

 grown in meat broth and other culture media elaborate 

 chemical poisons which, when injected into the lower animals, 

 induce in an acute form one or more of the symptoms char- 

 acteristic of the dissase caused in man by the microorgan- 

 ism. It is true that until quite recently this theory has 

 been opposed by some, and it is altogether possible that 

 at present there may be those who are not altogether con- 

 vinced of its truth. However, we are not acquainted with 

 any argument against it which remains unanswered. For 

 a while Baumgaeten claimed that the formation of chem- 

 ical poisons in the dead matter of meat broth and other 

 media by the germ does not prove that the same agent is 

 capable of forming the same or similar jiroducts within the 

 living body ; but the isolation of tetanine from the ampu- 

 tated arm of a man with tetanus, by Briegbe, furnished 

 the first positive answer to this criticism, and since that 

 time a number of bacterial poisons have been obtained from 

 the bodies of men and the lower animals. We now expect 

 to find each specific, pathogenic microorganism producing 

 its characteristic poison or poisons. The evidence on 

 this point will be given further on in a brief sketch of the 

 chemical factors in the causation of some of the best-known 

 infectious diseases. 



Before taking up the individual diseases, we will give 



