DISEASES OP THE SKIN 297 



skin against an ordinary wetting, and the prolonged action of 

 moisture is necessary to soak the cutaneous covering. It is 

 for this reason that the lower extremities, continuously 

 exposed to moisture, as the coronary region and heels of the 

 horse's hoof, more easily succumb to the action of excessive 

 cold. Another reason, and a potent one, why the lower 

 extremities exhibit frost bites, more commonly lies in the fact 

 that wounds of more or less consequence are often met with 

 in those localities. The cold lowers the vitality of the parts, 

 purulent bacteria always abound, they enter the wounds,' 

 multiply and are followed by more or less extensive necrosis 

 of the parts invaded by them. I really think that the vast 

 majority of so-called frost bites of the lower extremities in the 

 horse are no frost bites at all, but septic infections made pos- 

 sible by the lowered vitality of the tissues due to the exposure 

 to prolonged and excessive cold, which, when active as mois- 

 ture, macerates the epidermis, thus predisposing to infections. 



How does excessive cold affect the shin f 



Three degrees of freezing are recognized. 



What are the peculiarities of these three degrees ? 



First degree : Due to moderate cold acting temxjorarily. 

 The changes occurring in pigmented skin are either not to be 

 seen or are ill defined. The changes which take place are : 

 As the result of the action of the cold anemia of the skin sets 

 in as the arteries contract. Next the arteries dilate and the 

 venous circulation becomes gorged, for which reason the skin 

 appears dark red ; at the same time more or less swelling and 

 pain are present. 



Second degree : Due to a more persistent action of cold. 

 Here the same 'changes as above occur, only the exudation 

 under the epidermal layer is excessive, and consequently 



