SYSTEMIC INFECTIONS. 99 



many cases when a pre-existing local disease exists 

 at some point. In a small group of diseases 

 (typhoid, paratyphoid, pneumonia) this second- 

 ary general invasion occurs with great constancy, 

 and the organisms can always be cultivated from 

 the blood if this is undertaken at the proper time. 

 In syphilis general invasion occurs only after a 

 certain "incubation period" has been passed in 

 the primary sore, and after this time it exists as a 

 protracted blood infection. 



Others appear to be primarily and essentially 

 blood infections, little or no reaction taking place infections. 

 at the point of invasion. This is true of systemic 

 plague, anthrax, Eocky Mountain spotted fever, 

 some very virulent infections with the streptococ- 

 cus, relapsing fever, and in many of the protozoan 

 infections, as in malaria, piroplasmosis, and in 

 sleeping sickness. In some of these the organisms 

 may pass a portion of the incubation period 

 in the lymph glands, where they proliferate 

 to such an extent that they gradually over- 

 whelm the circulation in large numbers. The 

 organisms of malaria and piroplasmosis proliferate 

 in the blood-stream, i. e., within the erythrocytes. 

 It also seems probable that the other organisms 

 mentioned are able to proliferate in the plasma, 

 and that their presence in the blood-stream is not 

 due entirely to their continuous escape from such 

 solid organs as the lymph glands and spleen, or 

 from the point of primary invasion. They are true 

 or full parasites in the sense of Bail. 



From the standpoint of continuity there are sev- 

 eral types of systemic infection. 



We may, in the first place, recognize the continu- continnons 



i i XT. J?x x-u Systemic 



ous type, in which the organisms, after they once infections. 



