RELATIONS TO DISEASE. 483 



may be found in the brain and internal organs. In some 

 fatal cases with coma, the cerebral capillaries may appear to 

 be almost filled with them. 



Irregular types of fever, sometimes of a continued 

 character, may be produced by infection with different 

 generations of the same variety of parasite, or by different 

 varieties (mixed infections). In the various tropical 

 malarial fevers it is quite possible that there are still other 

 varieties of parasites whose characters have not yet been 

 worked out. 



Relations to the Disease. Though the malarial para- 

 sites have in no form been cultivated outside the body, 

 the evidence that they are the cause of the disease amounts 

 to a practical certainty. They are always present in the 

 disease, and have been found in no condition apart from 

 malaria. Their cycle of development also corresponds in 

 a remarkable manner with the course of the fever, each 

 febrile attack being accompanied by the appearance of a 

 new generation of parasites in the blood. In all probability 

 the fever is produced by toxic bodies set free by the young 

 parasites, but that cannot yet be directly proved. The 

 presence of the parasites in the red corpuscles and the 

 destruction of their substance which takes place, explain 

 the occurrence of the anaemia which so often results, the 

 subsequent distribution and storage of the altered haemo- 

 globin producing the pigmentary changes in the various 

 organs. 



The disease can also be communicated from one person 

 to another by injecting the blood containing the parasites. 

 Several experiments of this kind have been performed 

 (usually about i to i c.c. of blood has been used), and the 

 result is more certain in intravenous than in subcutaneous 

 injection. In such cases there is an incubation period, 

 usually of seven to fourteen days, after which the fever 

 occurs. The bulk of evidence goes to show that the same 

 type of fever is reproduced as was present in the patient 

 from whom the blood was taken. 



It may also be mentioned that in certain affections of 



