MALAEIAL ORGANISMS 189 



Plasmodium of Marchiafava and Celli. Recently, as the result of more exact 

 studies of blood parasites, Max Hartmann and Victor Jollos have worked out a 

 new classification. They have created a new order, Binucleata, in which are 

 united the various blood parasites, it being shown that the trypanosomes and 

 other forms living free in the blood-fluid are related to the plasmodii and con- 

 nected by intermediate forms. The malarial parasites are grouped in the family 

 Plasmodiidae and four genera are recognized. The genera Achromaticus and 

 Polychromophilus of Dionisi are parasites of bats, the genus Proteosoma Labbe 

 is parasitic in birds and the genus Plasmodium infests man, monkeys and 

 squirrels. All the Plasmodiidaj require two hosts to complete their life-cycles 

 and one of these hosts acts as the transmitting agent. Three species of Plas- 

 modium are generally recognized as affecting man, but some investigators be- 

 lieve that more species are concerned in producing the various types of malarial 

 fevers. The nomenclature of the malarial parasites is a most confusing one, 

 hardly two authors agreeing in the specific names applied to the different 

 parasites. We follow here the nomenclature of Blanchard who has carefully 

 worked out the synonymy according to the rules of zoological nomenclature. 



Plasmodium vivax (Grassi & Feletti). — This parasite produces the benign 

 tertian fever, simple or double. The period of schizogony is 48 hours and may 

 sink to 44 hours. It is the most widely spread and commonest of the species. 



Plasmodium malarice (Laveran). — This parasite produces the regular quar- 

 tan fever. The period of schizogony is 72 hours. It is more prevalent in tem- 

 perate and subtropical regions, but appears to be rare everywhere. It resembles 

 the Plasmodium vivax in its appearance and development, but can be dis- 

 tinguished readily by morphological differences, besides the different type of 

 fever that it produces in man. 



Plasmodium falciparum (Welch). — This is the parasite of pernicious, trop- 

 ical or sestivo-autumnal malaria. It is most frequently termed Plasmodium 

 prcecox or Laverania malarice. The genus Laverania is based on the crescent- 

 shaped stage but has been generally abandoned. The opinion has been expressed 

 by various investigators that there is more than one species of organism account- 

 able for the various forms of pernicious or quotidian fever. Schizogony usually 

 occurs in the internal organs, particularly the spleen, instead of in the peripheral 

 circulation, as is the case ^vith the tertian and quartan forms. The fever pro- 

 duced is of an irregular type and the period of schizogony, as it does not occur 

 in the periphery, has not been definitely determined. Most observations indicate 

 a period of about 48 hours, others one of 24 hours. 



THE UFE-CYCLE OF THE MALARIAL ORGANISMS. 



There are two cycles in the evolution of the malarial parasites. One takes 

 place in the blood, is asexual, and is designated the schizogonic cycle ; the other 

 is the sexual cycle which develops within the transmitter and is called the sporo- 

 gonic cycle.* The continuous existence of the parasites depends upon the trans- 



* The cycle in the blood is sometimes called endogenous, or cycle of Golgi, that in the 

 mosquito exogenous, or cycle of Ross. 



