CHAPTER XL. 



MALARIAL PARASITOLOGY. 

 Suborder: Hsemosporidia. 



THE causative agent of malaria is a protozoon which is classified 

 with the sporozoa (suborder: hoemosporidia). It is now universally 

 acknowledged to be the sole cause of what is properly included under 

 the somewhat misleading term of malaria, a term which signifies " bad 

 air." 



The actual discoverer of the protozoon is Laveran, who recognized 

 as early as 1880 the true nature of the dancing pigment which long 

 before him had been observed in intermittent fever. The relationship 

 of the paroxysm to the segmentation of the parasite was recognized 

 later by Golgi. Recently the relationship of certain insects to malarial 

 parasites has been demonstrated by Ross, and has been abundantly 

 confirmed by many. 



Before entering upon a description of these parasites in general, it 

 may be stated that they have a double cycle i. e., as a tapeworm 

 requires two hosts to complete its life cycle, so does the malarial proto- 

 zoon. The intermediate host in this case is a mosquito. At this day 

 there ought to be no more skepticism as to the role played by certain 

 mosquitoes; but one must not forget that it is a special genus, and 

 fortunately a relatively rare one, which causes the perpetuation of 

 these protozoa. The characteristics of this mosquito are such that even 

 people untrained in such observations can readily tell the malaria- 

 carrying mosquito from its relatively harmless and prolific simile. Hence, 

 a few useful points on the subject are given below. 



The cycle in the human being is known as the asexual cycle, or the 

 monogony ; while the primary cycle carried on in the viscera of the insect 

 is called the sexual cycle, or amphigony. There is undoubtedly in the 

 human being a third unknown step, a sort of hibernation or lying dor- 

 mant, attributable to a modification of a form which possibly belongs 

 to the monogony. 



In the asexual cycle the parasite grows and divides into segments 

 which correspond to the young form from which the parasite originates 

 without the influence of a sexual element. This process of apparently 

 agamogenetic division goes on periodically for a limited length of time. 

 It seems as if the power for self-reproduction is exhausted after a 

 time, and as if possibly also the blood of the host has formed circu- 

 lating compounds antagonistic to the parasite. These explanations for 

 the time limit seem reasonable. 



