NATURE AND CAUSATION. 163 



related — in some as cause, in others as effect — to other infec- 

 tive conditions which are surely propagated by contagion. 



In many of its principal features, which seem associated 

 with or owe their existence to a vitiated condition of the blood, 

 the result of the entrance into it of a specific morbific material, 

 this disease bears much resemblance to some other conditions 

 resulting from blood-changes or contaminations, as scarlatina 

 or 'purpura hcemorrhagica. As in these, there is a marked dis- 

 position to seize upon and exhibit peculiar blood-changes in 

 connection with mucous membranes ; while when they terminate 

 fatally, they all appear to reach that result by processes not 

 much dissimilar. 



In its mildest form, as simple cutaneous erysipelas, existing 

 as a diffuse spreading inflammatory action of a benign character 

 confined to the skin, it is not often met with ; more frequently 

 we encounter it in the form known as the phlegmonous or. 

 cellulo-cutaneous erysipelas of rather a malignant type, and in 

 which there is involved, to a greater or less extent, the sub- 

 cutaneous connective and other tissues. 



When appearing in the horse in the idiopathic form, one of 

 the hind extremities seems almost invariably selected as the 

 situation for the manifestation of the local phenomena, the 

 most characteristic of which in connection with the local in- 

 flammation is the peculiar serous exudation, which may either 

 occur uniformly distributed over a considerable surface of the 

 skin in the form of a copious perspiration, in which form it is 

 commonly found around the upper part of the hoof and in the 

 hollow of the fetlock, situations largely supplied with sebaceous 

 follicles, or projected on its surface in the form of considerable 

 vesicles or bulla3, which in the severer forms contain a bloody 

 serous fluid and are chiefly observed situated over the inner 

 surface of the thigh and hock, situations where, in the horse, 

 the skin is remarkable for its great tenuity. 



Along with this external cutaneous exudation there is in- 

 variably, to a greater or less extent, effusion amongst the sub- 

 cutaneous connective-tissue of serum or Hquor sanguinis. 

 Coincident with these changes, and with the infiltration of the 

 subcutaneous connective-tissue with inflammatory products, a 

 change of a somewhat similar nature is going on in the sub- 

 mucous layer of several of the mucous membranes. 



11—2 



