MICROBIAL DISEASES OF MAN AND ANIMALS. 667 



three days of the attack. The Commission of the French Government 

 studying yellow fever in Brazil showed that the virus passed through the 

 Chamberland filter marked "F," but that it was restrained by the Chamber- 

 land "B" unless the serum was diluted, in which case the virus passed 

 through the finer-pored Chamberland "B" filters. Heating for ten 

 minutes at 55 appears to destroy the virulence of serum taken from 

 infected individuals. 



As yellow fever is transmitted solely by the mosquito, modern methods 

 of combating the disease consist in the destruction of the mosquito and 

 careful screening of all dwelling houses in infected centers. As a result of 

 measures of this character, yellow fever has been eradicated from 

 Havana where it had remained endemic for many years prior to the dis- 

 coveries of Reed and his associates. 



DISEASES CAUSED BY PROTOZOA.* 



RHIZOPODA. 



The amoebae are the most important of the parasites belonging to the rhizopods. 

 Some amoebae are parasitic in the intestines of cattle, horses, mice, frogs, fish and 

 men; most of them, like Amoeba coli of man, are harmless. One species, Amceba 

 dysenteries (not Entamoeba histolytica) , produces a very severe disease of man. 

 Amceba meleagridis is the cause of a fatal disease of turkeys (p. 669). Another 

 amoeba is sometimes a harmful parasite of the human bladder. While still another, 

 Am&ba buccalis, is a harmless parasite which is frequently found about the teeth of 

 persons who do not keep their mouths perfectly clean. 



AMCEBIC DYSENTERY. 

 Amceba dysenteries. 



Distribution. Amoebic dysentery is most often a disease of tropical, 

 or sub-tropical, countries; but cases of it occasionally occur in Great 

 Britain and in Central Europe, and in the United States. 



The Parasite: Amosba coli (Fig. 117) and Amoeba dysenteries are both parasites in 

 the human intestine. Both are amoeboid organisms, measuring from 15^ to 30^ in 

 diameter. Their cytoplasm contains a nucleus, vacuoles, and food particles. Both 

 may multiply by budding and by simple division; sexual multiplication has not been 

 observed in either. Amceba coli may also reproduce by forming eight spores. Amceba 

 coli is distinguished from A mceba dysenteries by its spore formation and by its homo- 

 geneous cytoplasm; the outer layer of the cytoplasm of Amceba dysenteric is more 

 distinct and forms a resistant ectoplasm. It is probably because of this ectoplasm that 



* Diseases arranged genetically. 



* Prepared_by J. L. Todd. 



