INFECTION AND IMMUNITY. 457 



rhagic septicaemias." When running their normal 

 course these organisms cause typical septicaemias in sus- 

 ceptible animals ; but often, from causes not entirely 

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

 but ver}'^ 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 diseases that are properly classed as septi- 

 caemias, because of the usual general invasion of the 

 body by the organisms concerned in their production, 

 but which frequently assume a purely local character 

 — in both instances proving fatal to the animal in- 

 fected. From what we have seen it is manifestly 

 probable that, whether these diseases be designated as 

 septicaemias or toxaemias, death is produced in all in- 

 stances by the poisonous products resulting from the 

 growth of the infecting bacteria. In the case of typical 

 anthrax, and other varieties of septicaemia, the produc- 

 tion of this poison is associated with the general dis- 

 semination of the organisms throughout the body, while 

 in those infections often referred to as toxaemias, of 

 which diphtheria may be taken as a type, the poison is 

 produced by the organisms that remain localized at the 

 site of invasion, and is 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 bac- 

 teria 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 



