THE PATHOLOGY OF MALARIA 637 



from malarial infection, and "one would accordingly expect that 

 infection of the mosquitoes in the neighbourhood of native 

 settlements would be common. This has been found to be 

 actually the case, and it has accordingly been suggested that the 

 dwellings of whites should as far as possible be at some distance 

 from the native centres of population. 



So far as is known, none of the lower animals have been 

 found to take the place of man as intermediate host to the 

 parasites of malaria, but the possibility of such being the case 

 cannot be as yet definitely excluded. On the death of infected 

 mosquitoes the exotospores or sporozoites will become set free, 

 and therefore theoretically there is a possibility that they may 

 enter the human subject by inhalation or by some other means. 

 We have no facts, however, to show that this really occurs, and 

 the evidence already obtained establishes the bites of mosquitoes 

 as the most important if not the only mode of infection. 



It may also be mentioned as a scientific fact of some interest, 

 though not bearing on the natural modes of infection, that the 

 disease can also be communicated from one person to another by 

 injecting the blood containing the parasites. Several experi- 

 ments of this kind have been performed (usually about J to 1 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 from seven to fourteen days, 

 after which the fever occurs ; the same type of fever is re- 

 produced as was present in the patient from whom the blood was 

 taken. 



The Pathology of Malaria. While much work has been 

 done on the malarial parasite, relatively less attention has been 

 directed to the processes by which it produces its pathogenic 

 effects. It may be said that the organisms are not always 

 equally prevalent in the circulating blood, and at certain stages 

 tend to be confined in the internal organs. Some of the patho- 

 genic effects are probably associated with particular stages 

 in the life-cycle. Thus the pyrexia occurs when the stage of 

 schizogony is actively in progress. No opinion can be stated, 

 however, as to the cause of the fever, whether it is due to a 

 toxic process or to general disturbance of metabolism. We can 

 better explain the anaemia which is so pronounced in cases where 

 the disease is of long standing, and which is due to the actual 

 destruction of red blood corpuscles. The parasite in its sojourn 

 in these cells absorbs their pigment and thus destroys their 

 function ; this is further evidenced by the activity displayed by 

 the red marrow in its attempts to make good the loss sustained 



