INFECTION AND IMMUNITY. 399 



introduced into animals, but often, from causes not en- 

 tirely clear, the animals die with only local lesions, or 

 with but very few organisms in the internal viscera. We 

 see here conditions analogous to those observed in the two 

 experiments with anthrax, viz., we find a group of dis- 

 eases that are normally classed as septicaemias, because of 

 the general invasion of the body by the organisms con- 

 cerned in their production, but which frequently assume 

 a purely local character — in both instances proving 

 fatal to the animal infected. From what we have seen 

 it is manifestly probable, whether these diseases be 

 designated as septicsemias or septic troubles, or toxaemias 

 or toxic troubles, that death is produced in all instances 

 by the poisonous products resulting from the growth of 

 the infecting bacteria. In the case of typical anthrax, 

 and other varieties of septicaemia, the production of this 

 poison is associated with the general dissemination of 

 the organisms throughout the body, while in those infec- 

 tions often referred to as toxaemias, of which diph- 

 theria may be taken as a type, the poison is produced 

 by the organisms that remain localized at the site of in- 

 vasion, and is from thence disseminated throughout the 

 body by the circulating fluids. 



Infection thus far, then, appears to be a chemical 

 process. Through special investigations that have been 

 made upon the products of growth of certain pathogenic 

 bacteria, this opinion has received further confirmation ; 

 it has been found possible by the use of appropriate 

 methods to isolate, from among the mass of material in 

 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 symp- 



