326 INFECTIVE DISEASES. 



lymph and in variolous lymph. Numerous attempts to cultivate them 

 in nutrient media and in the living animal failed entirely, and the 

 identity of the bacilli could not be determined. Pfeiffer, Guarnieri, 

 Monti, Buffer, and Plimmer have drawn attention to structures in 

 lymph, which they believe to be of the nature of parasitic protozoa. 

 These bodies have been studied, more especially in the tissues. They 

 are four times the size of ordinary micrococci, and are found in the 

 clear vacuole in the protoplasm of epithelial cells. Whether they 

 are really parasites or altered anatomical elements has not been 

 determined. No other conclusion can be drawn from all these 

 observations, except that the nature of the contagium of cow-pox 

 is unknown. 



ORIGIN OF COW-POX. 



Jenner's original theory was that cow-pox . was derived from 

 " grease," but subsequently he distinguished between cow-pox, a 

 disease peculiar to the cow, and " grease," a disease transmitted to 

 the cow from the horse, and the mistake of confounding these two 

 diseases was attributed to farmers and farriers. Thus he wrote : 



" From the similarity of symptoms, both constitutional and local, 

 between the cow-pox and the disease received from morbid matter 

 generated by a horse, the common people in this neighbourhood 

 when infected with this disease, through a strange perversion of 

 terms, frequently called it the cow-pox." 



Jenner's theory of the origin of cow-pox has been discouraged ; so 

 also has the view of its being a " spontaneous " disease in the cow, 

 though Ceely, after many years of research in the Yale of Aylesbury, 

 could never discover the probability of any other origin. Both 

 opinions have given way to the theory that cow-pox is small-pox 

 transmitted to the cow an opinion advocated by Baron, and 

 supported by an erroneous interpretation of Ceely's and Badcock's 

 variolation experiments. Thus the cow-pox and grease of farmers 

 and farriers no longer attracted attention in this country, and as 

 natural cow-small-pox has never been discovered, cow-pox has been 

 credited with being extinct. 



For a full discussion of this subject the reader is referred to the 

 work by the author on the History and Pathology of Vaccination, 

 but the variolation experiments alluded to will be briefly mentioned. 



In 1801 Gassner inoculated eleven cows with small-pox lymph, 

 and succeeded in one in producing phenomena indistinguishable from 

 the results of ordinary vaccination with cow-pox, and children were 

 inoculated from the cow. 



