MALARIAL PARASITOLOGY 501 



At all events the sporulat ion ceases after a while, and there arc distinct 

 changes in the morphology of the parasite. Finally, certain bodies are 

 formed which do not segment, and it is these which will now be described 

 in detail. They are known as gametes, or sexual forms, and represent a 

 male and female element which, however, cannot conjugate in the human 

 blood. When certain species of mosquitoes imbibe blood containing 

 such gametes, the process of conjugation is carried on in the chyme 

 stomach of the insect. How this proceeds will be described presently; 

 suffice it to say here that cysts are formed in the stomach wall of the 

 insect, which when matured discharge an enormous number of fila- 

 mentous sporozoites into the body cavity of the mosquito, whence they 

 reach what is usually called the salivary gland of the insect. From this 

 gland it is but a step to the proboscis, and when the insect thus infected 

 "bites" a human being numerous sporozoites pass into the circulation. 

 Just how these sporozoites are transformed into the well-known young 

 form seen on the red corpuscle is not known. 



While these processes are rather fully understood, the relapses of sup- 

 posedly cured cases are shrouded in mystery. The observations tend to 

 show that there is a difference in the parasites of relapses when compared 

 with those of a recent primary infection, and for my part I do not usually 

 have any difficulty in telling the parasites of relapse from those of a recent 

 primary infection. Moreover, I have also found that the parasites of a 

 supposed second infection resemble those of a relapse, and in the light of 

 this observation I doubt if a second infection in the proper sense of the 

 word is ever possible within a certain length of time. It is not within the 

 scope of this article to give a detailed description of the forms which in 

 my opinion point to a relapse ; suffice it to say that the parasites in ques- 

 tion show a tendency to remain dwarfed, and show fewer chromatin 

 bodies and greater irregularities in division than those of what I term a 

 recent primary infection. These abnormalities may be referable to the 

 persistent effect of antibodies. One form of parasite is so constant in 

 protracted cases and differs so much from the ordinary gamete that a 

 special description will be given. 



The different varieties of malarial and kindred parasites in man 

 and animals have, as might be expected, much in common. Hence 

 a general description of the cycle of one form will suffice to elucidate 

 the cycle of the others. 



Generalities of Cycle. A young, amoeboid, colorless, more or less 

 rounded parasite, measuring approximately two microns in diameter, 

 is seen attached to a red corpuscle. After a certain length of time, 

 usually a few hours later, granules or rodlets of pigment make their 

 appearance; these granules represent the haemoglobin on which the 

 parasite has been feeding, and it is now transformed into what is com- 

 monly termed melanin. They will be seen to be in passive motion, the 

 degree of motility depending upon the currents in the protoplasm in 

 which they are embedded, and they vary in the different varieties and 

 at different stages of the asexual phase. After a further lapse of time 

 this pigment is seen to gather centrally and evidences of cell division 



