462 SMALLPOX AND VACCINATION. 



for believing that vaccinia and variola are the same disease, 

 and that the differences between them result from the 

 relative susceptibilities of the two species of animals in which 

 they naturally occur. 



With regard to the relation of cowpox to horsepox, it is 

 extremely probable that they are the same disease. Some 

 epidemics of the former have originated from the horse, but 

 in other cases such a source has not been traced. Cattle 

 plague from the clinical standpoint, and also from that of 

 pathological anatomy, resembles very closely human small- 

 pox. Though each of the two diseases is extremely in- 

 fectious to its appropriate animal, there is no record of cattle 

 plague giving rise to smallpox in man or vice versa. When 

 matter from a cattle plague pustule is inoculated in man, a 

 pustule resembling a vaccine pustule occurs, and further, 

 the individual is asserted to be now immune to vaccination ; 

 but vaccination of cattle with cowpox lymph offers no 

 protection against cattle plague, though some have looked 

 on the latter as merely a malignant cowpox. Sheep-pox 

 also has many clinical and pathological analogies with 

 human smallpox, and facts as to its relation to cowpox vac- 

 cination "similar to those observed in cattle plague, have 

 been reported. Smallpox, cowpox, cattle plague, horsepox, 

 and sheep-pox, in short, constitute an interesting group of 

 analogous diseases of the true relationships of which to one 

 another we are, however, still ignorant. 



Micro-organisms associated with Smallpox. Burden 

 Sanderson was among the first to show that in vaccine 

 lymph there were certain bodies which he recognised as 

 bacteria. Since then numerous observations have been 

 made as to the occurrence of such in matter derived from 

 variolous and vaccine pustules. In especially the later stages 

 of the latter, many of the pyogenic organisms are always 

 present, e.g., staphylococcus aureus and staphylococcus cereus 

 flavus, and many of the ordinary skin saprophytes also are 

 often present, but no organism has ever been isolated which 

 on transference to animals has been shown to have any 

 specific relationship to the disease. A bacillus, however, 



