652 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 

 COWPOX, HORSEPOX, AND SHEEPPOX.* 



Variola refers to a condition of disease in man and animals, character- 

 ized by fever and the appearance of skin eruptions which successively 

 assume the form of papules, vesicles and pustules. The disease is fre- 

 quently found in the human species (smallpox), cattle (variola vaccinia, 

 cowpox), horses (variola equincB, 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 occasional 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 remarkable discovery relative to smallpox vaccination. 



Many attempts have been made to isolate the specific 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, MacGrath, 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 bodies in collodion capsules 

 in the peritoneal cavities of experimental animals. According to some 

 investigators the virus has been passed through a Chamberland filter. 

 The failure conclusively to discover the causative factor, according to 

 the present methods, may be due to the incultivability or unstainability 

 of the specific agent. 



* Prepared by W. E. King. 



