MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 805 



Berkefeld and Chamberland F cylinders, but not through the Chamber- 

 land B cylinder. 



COWPOX, HORSEPOX, AND ShEEPPOX* 



Variola refers to a condition or disease in man and animals, charac- 

 terized by fever and the appearance of skin eruptions which succes- 

 sively assume the form of papules, vesicles and pustules. The disease 

 is frequently found in the human species (smallpox), cattle {variola 

 vaccinia, cowpox), horses (variola equinas, horsepox) and sheep {variola 

 ovina, sheeppox). It is possible that some other species may be 

 susceptible. 



On account of the fact that vaccination of man with virus from cases 

 of cowpox affords remarkable protection against smallpox, it appears 

 reasonable to believe that cowpox virus or smallpox vaccine is a 

 modified form of smallpox virus. This fact, together with the occa- 

 sional positive results of various experiments in which other species 

 of animals have at times evidenced susceptibility to cowpox virus, 

 strongly suggests the possible etiological relationship of the diseases in 

 different species to each other and to smallpox in man. However, 

 conclusive proof supporting this suggested relationship does not exist. 

 The specific causative factor of smallpox or of cowpox is not known. 



Cowpox is a very common disease, perhaps having been prevalent 

 in England and Europe for centuries. Its presence has frequently 

 been observed in various countries since 1796 when Jenner contributed 

 to the world his important discovery relativeto smallpox vaccination. 



Many attempts have been made to isolate the causative 

 factor of cowpox. Early investigators frequently secured mixed and 

 pure cultures of various organisms, including different species of 

 micrococci, streptococci and bacilli from vaccine lymph. None of 

 these organisms were peculiar to the virus, and at present there exists 

 no definite evidence that the infectious agent of vaccine lymph is of 

 bacterial nature. Pfeiffer, Guanieri, Plimmer, Councilman, Mac- 

 Grath, Brinckerhoff and others, after observing the presence of apparent 

 cellular elements, or relatively large flattened bodies in vaccine lymph, 

 have suggested the possible protozoan nature of the causative agent. 

 Attempts have been made, with more or less success, to cultivate these 



* Prepared by W. E. King. 



