598 MALARIAL FEVER 



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 

 the apyrexial stages the total number of leucocytes may be 

 diminished, but that there is always an increase of the mono- 

 nuclear cells, these frequently numbering 20 per cent, of the 

 whole, and sometimes even outnumbering the polymorphs. 

 This is such an important feature that in cases where the 

 parasites themselves cannot be demonstrated in the blood, the 

 mononuclear reaction along with the presence of pigment in the 

 mononuclear cells (due to phagocytosis of pigmented parasites), 

 has been taken as evidence that the case is really one of malaria. 

 The mononuclear reaction is specially interesting from the fact 

 that in other protozoal diseases an activity of the same elements 

 has been observed. 



The question of the possibility of immunity to malaria being 

 developed naturally arises, and this is especially interesting in 

 the light of the leucocytic reaction which we have seen must be 

 looked on as an element in immunity against bacterial infection. 

 With regard to Europeans developing immunity, it is difficult to 

 speak. In such a malaria-stricken region as the West Coast of 

 Africa, the death-rate in residents of more than four years' 

 standing is less than in the previous years, but this may be due 

 to the survival of the more resistant immigrants. But there can 

 be little doubt that malaria in the negro is a much less serious 

 condition than in the European. Koch from his observations in 

 New Guinea attributes this to the infection of the native children 

 leading to the development of immunity in the adult community. 

 He found, what has been independently noted by Stephens and 

 Christophers in West Africa, that the greater number of the 

 children harboured malarial parasites in their blood. The wide- 

 spread presence of parasites in children might appear to preclude 

 the immunity of the adult being due to survival of the most 

 resistant, but the infant mortality in these regions may be very 

 high, and such a survival may be the real explanation. On the 

 other hand, Koch states that while an immunity appears to exist 



