488 VETERINARY BACTERIOLOGY 



Virus of the Poxes 



Disease Produced. Small-pox in man, cow-pox, sheep-pox, 

 horse-pox, swine-pox, goat-pox. 



There is much doubt relative to the position of the virus of the 

 various poxes. They are included in this group tentatively, as it 

 is found that the contents of the vesicles of the eruptions may be 

 filtered through a thin, coarse porcelain filter under pressure with- 

 out losing their infectivity. The causal microorganisms are, at 

 some stages, at least, filterable and probably ultramicroscopic. 

 Certain cell inclusions have been described as being probably of 

 protozoan nature, but the subject cannot be said at present to be 

 completely elucidated. The protozoan parasite has been named 

 Cytorhyctes vaccince in man. 



Immunity. Recovery from an attack of variola is accompanied 

 by a relatively permanent immunity. Vaccination is, therefore, 

 commonly practised, particularly against small-pox in man. The 

 attenuated virus in this instance is secured by passage through 

 an animal, usually a cow. The vaccinating material is the lymph 

 from the vesicles produced on the animals. It is inoculated into 

 the skin by scarification. The virulence is apparently very 

 greatly decreased by this method of inoculation, so that a relatively 

 mild type of disease is produced which terminates in immunity 

 being established. To what this immunity may be due is not 

 known. 



Virus of Yellow Fever 



Yellow fever in man has been shown to be due to a filterable 

 virus, probably an ultramicroscopic organism. All efforts at 

 cultivation have failed. The disease is spread only through the 

 bite of mosquitos that have taken virulent blood. The organ- 

 ism evidently undergoes a part of its life-cycle in the blood of the 

 mosquito (Stegomyia), for the latter does not become infective 

 itself for several days. It is evidently more than a mere 

 mechanical transfer of the organism by the mosquito; the latter 

 serves as a true intermediate host. 



Virus of Epidemic Infantile Paralysis 



Disease Produced. Acute poliomyelitis, Il< ine-Medin disease 

 in children. 



