38 TROPICAL MEDICINE AND HYGIENE 



each other, consequently parasites of intermediate ages 

 are rarely met with. The sporulation of these parasites 

 leads to rupture of the red corpuscles, when the spores, 

 together with the remains of the parasites, pigment, and 

 any other products of the metabolism of the parasites, are 

 set free in the plasma. 



The simplest explanation of the observed clinical 

 phenomena is that amongst these varied products are 



(1) toxins that act on the heat-controlling centre, 



(2) haemolytic toxins, variable in amount, and (3) toxins 

 affecting innervation. Blood serum taken before a rigor 

 and passed. through a Berkefeld filter will, when injected 

 into a healthy man, cause a febrile paroxysm similar to 

 that which occurs in malaria. Of the bodies set free, 

 the spores rapidly enter other red corpuscles, and recom- 

 mence the cycle, or failing to do this are destroyed by 

 phagocytes or by the blood plasma, and this destruction 

 is facilitated by the action of quinine. The pigment is 

 taken up by the leucocytes, usually by the large mono- 

 nuclear or hyaline cells, and ultimately deposited in the 

 spleen, which becomes, in a chronic case, of a deep 

 slate black colour. It is also deposited in the connective 

 tissue cells of the liver. In an earlier stage the spleen 

 may merely appear to be congested, but on microscopic 

 examination abundant deposits of pigment will be seen 

 even then. 



The symptoms, therefore, are toxic, and the severity 

 will in part be due to the amount of the toxin, which 

 depends in the main on the number of parasites present. 

 Parasites may be present in small numbers without 

 causing pyrexia, though usually malaise, and perhaps 

 anaemia, will be caused. 



The actual number of parasites required to cause fever 

 has been estimated by Gray and, by a more accurate 

 method, by Ross. The numbers can only be considered 

 as approximate, and probably vary in different persons. 

 The usual limit pyrogenic limit according to these 

 observers is about 250 per cubic millimetre ; as the 



