PLASMODIUM 



505 



Polymitus form because of its flagella. Later Laveran repudiated 

 this term, which, indeed, could not be used, because it had already 

 been applied to a plant. He then suggested the term ' hgematozoon,' 

 but this is objectionable, because the hsematozoa are a group of 

 parasites, and not a single genus. Metchnikoff suggested the term 

 Hcematophyllum malaricB, which is equally impossible; therefore the 

 earliest distinctive term is ' Plasmodium' which Was used by 

 Marchiafava and Celli in 1885. 



It is not a good term, because a Plasmodium is generally con- 

 sidered to be a mass of protoplasm with several nuclei representing, 

 not one single animal, but several. 



General Account. — 'The malarial parasites may be taken as the 

 typical examples of the Plasmodidae. 



The malarial parasite exists in nature outside the human body 

 in certain species of different genera of the family Anopheliase, 

 a type of mosquito which is somewhat easily identified by its 

 habit of projecting at almost right angles from the surface on which 

 it stands. In the salivary glands of infected insects the malarial 

 parasites are found as fine fusiform bodies, about 10 to 20 in length, 

 and I to 2 ^ in breadth, lying in the cells or in the duct. These 

 fusiform bodies are called sporozoites, and consist of cytoplasm 

 containing a central nucleus composed of chromatin. 



The ends of the parasite are pointed, one being sharper than the 

 other. They are capable of movement forwards, and of flexion into 

 loops or curves. It may be that the sporozoites represent male, 

 female, and indifferent parasites, or they may not; the question 

 is still undecided. 



When inoculated into man by a mosquito, they penetrate into the 

 red blood cells, and develop into small endo-corpuscular parasites 

 called the trophozoites, which at first are composed of cytoplasm and 

 a nucleus. 



This young trophozoite grows, throwing out pseudopodia for the 

 purposes of nutrition, and presently a vacuole appears, converting 

 the small parasite into a ring form, which, according to Schaudian, 

 is of benefit in enabling it to absorb nutriment quickly. 



The vacuole does not keep pace With the growth of the parasite, 

 and finally in the old form disappears. Early in the ring forms 

 there appear granules of a black pigment, Which used to be called 

 melanin, but Which has by no means the chemical characteristics 

 of true melanin, as will be described under Malaria. This pigment 

 has been named by Sambon ' hsemozoin ' — a name which appears to 

 us to be peculiarly suitable, and will therefore be used in this work. 

 It is really of an excrementitious nature. The fully-grown tropho- 

 zoite now ceases to be amoeboid, and, becoming rounded off and 

 full of pigment granules, is called the schizont, which has a subcentral 

 nucleus. This nucleus now divides, so that parasites may be seen 

 with two, three, four, fi.ve, six, up to twenty-four nuclei. The 

 cytoplasm around these nuclei segments into small bodies called 

 merozoites, each with a nucleus, but an unsegmented portion 



