THE PATHOLOGY OF MALARIA 533 



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 parasite 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 pa.rasites. 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 probably at 

 certain stages tend to be confined in the solid organs ; thus they 

 may be scanty at the height of the paroxysm. Some of the 

 pathogenic effects are probably associated with particular stages 

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

 sporulation 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 

 by the blood. One of the most interesting events in malaria, 

 and one that links it with bacterial infections, is the reaction of 

 the colourless cells of the blood. It has been shown that during 



