766 



PATHOGENIC PROTOZOA 



first cold weather. Relapses continue to occur throughout the winter 

 season. Modern times have seen it disappear from many regions 

 where it was f ormerly'endemic, because of increased cultivation of the 

 soil and better surface drainage, as, for example, in England and the 

 Ohio river valley. 



In the registration area of the United States there were 1,565 

 deaths from malaria in 1913 ; in Italy, up to 1900, the average number 

 of deaths from this cause annually was 16,000. One cannot obtain a, 



FIG. 183. PLASMODIUM VIVAX. 

 (Army Med. School Collection, 

 Washington, D. C.) 



FIG. 184. PLASMODIUM VIVAX. (Gamete.) 

 (Army Med. School Collection, Washing- 

 ton, B.C.) 



true picture of the importance of the disease, however, from mortality 

 statistics, since it is not often fatal, and the morbidity is out of pro- 

 portion to the mortality. In many villages, where it is endemic, one- 

 third to one-half the population may have parasites in the blood, most 

 of them without clinical symptoms, yet they are not able to work and 

 the children remain undeveloped and backward. Much of the illness 

 attributed to hookworm infection is, in reality, due to latent malaria. 

 The parasites belong to the class of hemosporidia, and are closely 

 related to the coccidia, which are parasites of epithelial cells, while 

 the plasmodia are parasitic on red-blood cells. There are two divisions 

 of the life cycle ; that which occurs in man, the endogenous, asexual 

 or schizogenous, and that which occurs in the mosquito, the exogenous, 

 sexual or sporogenous; for this reason the mosquito is the definitive 

 and the man the intermediate host. 



