DEVELOPMENT OF THE MALARIAL PARASITES OF MAN 159 



It is of importance to record that, although malarial parasites occur in mammals 

 {monkeys, bats, etc.) the human ones are not transmissible to mammals, not even to 

 monkeys. The species, therefore, are specific to the different hosts (Dionisi, Kossel, 

 Ziemann, Vassall). 



An important work dealing with the modern applications of the mosquito-malaria 

 theory in all parts of the Tropics was published by Sir Ronald Ross in 1911. It is 

 entitled "The Prevention of Malaria" (John Murray, London, 2is.). 



DEVELOPMENT OF THE MALARIAL PARASITES OF MAN. 



The commencement of the developmental cycle and of the infection 

 of man, is the sporozoites (fig. 80, /) which are passed into the blood 

 of a person by the bite of an infected mosquito. Prior to this the para- 

 sites collect in the excretory ducts of the salivary glands (fig. 80, 27) 

 -of the Anopheles. The sporozoites are elongate and spindle-shaped, 

 10 /A to 20 ^ long and i //, to 2 //, broad, with an oval nucleus situated 

 in the middle. They are able to glide, perform peristaltic contractions, 

 or curve laterally. Schaudinn has studied the penetration of the red 

 blood corpuscles (fig. 80, 2) by the sporozoites in the case of the 

 living tertian parasite. The process takes forty to sixty minutes in 

 drawn blood. After its entrance the parasite, which is now called a 

 trophozoite, contracts, and becomes an active amcebula (fig. 80, 3). 

 It develops a food vacuole and grows at the expense of the invaded 

 blood corpuscle (fig. 80, 4), which is shown by the appearance of 

 pigment granules (transformed haemoglobin) in it. When the maxi- 

 mum size is attained, multiplication by schizogony (fig. 80, 5-7) begins 

 with a division of the nucleus, which is followed by further divisions of 

 the daughter nuclei, the number of which varies up to 16 or even 32, 

 depending on the species of the parasite. Then the cytoplasm divides 

 into as many portions as there are nuclei, the result being a structure 

 suggestive of the spokes of a wheel or of a daisy, the centre of the 

 resulting rosette being occupied by dark pigment. Finally, the parts 

 separate from one another, leaving behind a residual body contain- 

 ing the pigment, and the daughter forms issue into the blood plasma 

 as merozoites (fig. 80, 7). They are actively amoeboid (fig. 80, 8) and 

 soon begin to enter other blood corpuscles of their host, for the entry 

 into which thirty to sixty minutes are necessary, according to 

 Schaudinn's observations. 1 



Here they behave like sporozoites which previously entered and 



1 It should be remembered that some authors (Laveran, Argutinsky, Panichi, Serra) argue 

 against the intra-globular position of malarial parasites and state that they only adhere out- 

 wardly to the red blood corpuscles. These views have recently been revived by Mary Rowley- 

 Lawson, and she states that the malarial parasite is " extracellular throughout its life-cycle and 

 migrates from red corpuscle to red corpuscle destroying each before it abandons it." (fourn. 

 Exper. Mcd., 1914, xix, p. 531.) 



