858 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



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 relative to 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 

 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 to discover the causative 

 factc-r, according to the present methods, may be due to the inability 

 of microbiologists to cultivate or stain the specific agent. 



Cowpox is characterized by eruptions which usually occur on the 

 skin of the teats and udder. The material contained in these pustules 

 is transferred to other animals by the hands of the milker and through 

 other possible means of dissemination. The chief channel of infection 

 appears to be through an abrasion in the skin. The period of incuba- 

 tion of cowpox is about two days. The virus possesses relatively weak 

 resistance to heat, light and chemicals. The control of the disease 

 depends chiefly upon precautions relative to the transmission of the 

 virus on the hands of the milker from infected to healthy cows. 



Horsepox may be diagnosed by the appearance of the characteristic 

 pustules usually upon the skin, nasal mucosa and buccal membrane. 



Sheeppox is characterized by the presence of the typical skin 

 eruptions, following a rise of temperature. 



DENGUE* 



This disease (break-bone fever) of man occurs in all parts of the 

 world. It is characterized by a sudden attack, intense prostration 



* Prepared by M. Dorset. 



