386 CLINICAL BACTERIOLOGY. 



malarial blood. Subsequently, infection was repeatedly 

 transmitted with the blood of malarial patients by subcuta- 

 neous and intravenous injection. Malaria is, however, not 

 a contagious disease. It does not pass from one human 

 being to another under natural conditions. This could only 

 be possible if the blood of a malarial patient gained en- 

 trance into the body of another individual; and probably 

 few opportunities for this are afforded. The parasites are 

 not present in the secretions and excretions of malarial 

 patients ; they appear to be present in the contents of the 

 herpetic vesicles that malarial patients often exhibit. At 

 least, malaria has been inoculated by means of the contents 

 of such vesicles. 



The malarial parasites must, however, be present some- 

 where in nature. They must live in some form in air, earth, 

 or water, in certain swampy regions in which the disease 

 is endemic, and at certain times becomes epidemic. The 

 view is generally held that the parasites are inhaled ; some 

 believe that they are taken up with the drinking-water. 

 Transmission through the bites of insects is theoretically 

 possible, and is admitted by some observers, but it is not 

 yet demonstrated.* 



The period of incubation is in most cases from eight to 

 fourteen days ; cases are, however, known in which the 

 disease appeared months after infection, and others in which 

 the period of incubation was only one or two days, or even 

 hours. These differences may be explained by the num- 

 ber of the infecting germs, and by the varying individual 

 predisposition of those infected. That the germ is taken 

 up in a form that must pass through certain variations 

 within the body in order actually to become the malarial 

 parasite is negatived by the cases with a short period of 

 incubation. 



The Action of Quinin and Spontaneous Recovery from 

 Malaria. Lave ran has determined that addition of even a 

 very dilute solution of quinin to a blood-preparation at 

 once causes cessation of the ameboid movements of the 

 parasites. Within the human body, also, the parasites un- 

 dergo visible alterations after administration of quinin : they 

 suffer in motility and undergo degeneration, and, in many, 

 sporulation does not take place in the normal manner. 



* Recent observations have demonstrated most conclusively that malaria is 

 transmitted by some varieties of mosquitoes. A. A. E. 



