748 Mr. Henry George Plimmer [May 2, 



likeness between this and the parasite causing human malaria— to 

 deduce from the one the etiology of the other, which was confirmed 

 by Grassi and others. The Plasmodium precox is, in many stages, 

 so like human malaria that it can only be differentiated by the 

 presence of the oval nucleus of the bird's red corpuscles. The hfe- 

 cycle is very complex, part taking place in the blood of the bird, 

 and another part (sexual reproduction) in the body of a mosquito. 

 This parasite was first seen by Grassi in 181)0 ; it is very widely 

 distributed, and is very deadly to birds. 



Human malaria has been known for centuries. Yarro, who knew 

 a good deal about what we should now call hygiene, more than a 

 century B.C., thought that malarial fevers were due to invisible 

 animals, which entered the body with the air in breathing, and 

 Vitruvius, Columellus and Paladius were of the same opinion. Now 

 we know that the mosquito is again the carrier, and that the sexual 

 part of the parasite's cycle takes place in it, but whether the mosquito 

 alone can account for all the phenomena of malaria is not yet quite 

 certain. 



There are three varieties of malaria in man— the tertian, quartan, 

 and quotidian ; in the tertian the cycle of the parasite in the body 

 takes forty-eight hours, and in quartan seventy-two hours, and in 

 pernicious malaria the fever is very irregular, but continuous. Whether 

 there are three different parasites, or only one. which is altered accord- 

 ing to its environment of host, climate, etc., is still apparently uncer- 

 tain. Laveran and Metchnikoff believe in the specific unity of the 

 parasite, whereas some observers want as many as five different 

 species. 



Just as in human malaria the pernicious form is distinguished by 

 the elongated form of its gametes, so in bn-ds there is a parasite which 

 is distinguished, in the same way, from Plasmodium prsecox by its 

 very elongated gametes. This parasite is called Hsemoproteus 

 Danilewski. Its development is unknown ; it begins as a tiny 

 irregular body in the red corpuscles of the bird, then it grows in the 

 long axis of the cell and turns round the end of the nucleus. It is 

 possible in these parasites to follow the process of impregnation, which 

 normally takes place in some insect. By taking the blood when full 

 of the long, fully-grown gametocytes, and keeping it for a time out- 

 side the body, this process can be followed. 



First of all, the gametocytes escape from the blood-corpuscles and 

 roll themselves up into a ball. Some of these remain quiet — the 

 females, curiously, the macrogametocytes — whilst in the microgame- 

 tocytes active movements are seen ; then tailed processes are seen 

 projecting from its surface, which at last get free and wander about 

 in tlie blood, this constituting the origin of the microgametes from 

 the microgametocyte. They then find a macrogamete, and penetrate 

 into it and fertilize it. This fertilized macrogamete then alters its 

 shape and becomes an ookinete, with the remains attached containing 

 the pigment. It may enter a red corpuscle, but it usually breaks up, 



