502 PROTOZOA 



can then be made out; there may be a distinct rosette-like arrangement 

 or not. The next step is the breaking up of the parasite into segments 

 free from pigment. The further observation of these segments, each 

 of which represents a young parasite, identical with the young form 

 from which its progenitor was built up, is a matter of difficulty. I had 

 the good fortune of watching one in a fresh-blood preparation from 

 the moment of its detachment from the mother substance, and saw it 

 approach corpuscle after corpuscle. Its movements were gregarine- 

 like. It did not attach itself to a corpuscle within an hour, presumably 

 because of the change in the nature of the blood and its plasma. 



In the blood stream it is but rarely seen free in the plasma, and it 

 would appear that it rapidly attaches itself to a neighboring corpuscle. 

 That would tend to explain the fact that in certain forms of malaria 

 it is not an uncommon thing to find several parasites in one corpuscle; 

 this is seen especially in those cases where segmentation takes place 

 in the bone-marrow, and where on account of the absence of the velocity 

 of the blood stream the parasites are less apt to be scattered than in 

 the circulating blood. 



It is to be remembered that the process of growth and division can- 

 not be readily observed in all the forms of malaria because certain 

 parasites complete their asexual cycle in the viscera, chiefly also, it 

 seems, in the bone-marrow and spleen. 



Three types of parasites are recognized. Classified zoologically they 

 are: Plasmodium vivax (tertian), malarise (quartan), and praecox 

 (sestivo-auturnnal) . 



The life cycle of each presents certain characteristics which hold it 

 apart from the others. Some authors suggest a unity of parasites, but 

 the mere fact that the gametocytes of tertian and aestivo-autumnal fever 

 differ absolutely from each other is a capital reason why this is improb- 

 able; there are many other striking differences. 



A brief consideration of the salient facts follows : 



Plasmodium Vivax, the Parasite of Tertian Ague. 



The young form is more difficult to find and to recognize than any 

 of the other forms. A pale area is seen on an otherwise unaltered red 

 corpuscle, situated usually eccentrically, about one-tenth the size of 

 the red corpuscle or about one-fourth its diameter, when at rest pre- 

 senting a rounded appearance, usually actively amoeboid, throwing out 

 pseudopodia which are distinct, never remaining long in the same focal 

 plane, frequently dipping, so to speak, into the substance of the cor- 

 puscle. It is often called the hyaline form because it is free from 

 pigment, but it is not hyaline in the proper sense of the term. It is 

 also called the ring form, because of its resemblance to a ring in stained 

 preparations; but it is never a true ring. 



The forms intermediate between this and the segmentation stage 

 are simply larger parasites, which are readily found on account of the 

 pigment granules which they contain. 



