666 INFECTIOUS DISEASES. 



COWS unless they had been accidentally inoculated through the medium 

 of the people about the farm. Unfortunately, he named the pustular 

 disease of the horse which he had studied "sore heels," and for a 

 long time all those who busied themselves with the question of vaccine 

 confounded *' sore heels " with a number of different diseases, although 

 as early as 1802 Loy had experimentally proved that so-called " grease " 

 (in reality horse-pox) was transmissible by inoculation to the cow, in 

 which it produced cow-pox. 



Ley's "grease" and Jenner's "sore heels" only represent forms 

 of horse-pox, but for more than fifty years the origin of vaccine was 

 sought in grease, lymphangitis, and other diseases which attack the 

 extremities of horses' limbs. P^telard (1845-1868) rediscovered and 

 redescribed horse-pox and proved its transmissibility to man; Lafosse 

 and U. Leblanc discovered it in an epizooty which broke out at 

 Eieumes ; and Bouley in 1862 furnished a synthetical description of it 

 under the designation of horse-pox. He shows that horse-pox is always 

 a pustular disease, but that it may sometimes appear in the form of 

 a discrete eruption around the lips and nostrils, sometimes of an erup- 

 tion limited to the pasterns or extremities of the limbs when inoculation 

 has been effected in this region, sometimes of lymphangitis, and some- 

 times of a more or less confluent and generalised eruption. 



Symptoms. The disease as discovered and described by Jenner 

 was soon rediscovered and redescribed on all sides — by Sacco in Italy, 

 Hering in Germany, etc. 



The pustular eruption usually appears on the udder in the case 

 of cows, and on the muzzle, nose, and lips in that of calves. In 

 exceptional cases the eruption may become generalised. 



The pustules are round or slightly elliptical, and are preceded by 

 the appearance of red congested patches, followed by infiltration and 

 thickening of the skin. 



The pustule is moderately prominent, and after some days there 

 is exudation at its centre, transforming it into a vesico-pustule. The 

 exuded liquid collects under the thickened layer of epidermis, which 

 it raises, and on examination it appears as a white or transparent 

 little central patch, with a thin grey periphery surrounded by a reddish 

 inflammatory zone. This liquid becomes thicker and the pustule is 

 flattened at its centre, then, towards the eighth or ninth day, the 

 pustule is ruptured, owing to tearing of the epidermic patch. The 

 vaccine thus escapes. 



In what is termed spontaneous vaccinia the udder is covered with 

 a varying number of pustules, usually in different stages of development. 

 Some are very small, whilst others have attained the size of sixpence 

 and are already in course of cicatrisation. 



