RINGWORM. 051 



detached, exposes the dermis, which is swollen and bleeding. Gradu- 

 ally the centre becomes detached, whilst the periijhery, representing 

 a more recent lesion, continues to adhere. The crusts then rest on 

 a thin layer of pus, and the dermis, whilst still inflamed, is punc- 

 tuated with numerous minute apertures, representing the roots of the 

 detached hairs. The pus lifts the crust ; gradually it dries up and 

 forms superposed layers, which may or may not prove adherent to 

 the parasitic products, and which form a new crust. The latter is 

 purely inflammatory in character, and is left after the fall of the 

 first. It no longer contains any parasites, at least within its 

 deeper layers. 



This second crust dries up in its turn, falls away or breaks up, 

 leaving a smooth spot, over which the hairs again appear, either at 

 once, or at least after a short period of desquamation. 



The disease is accompanied by well-marked pruritus, more marked 

 at the commencement and towards the end than during the inter- 

 mediate period, but, nevertheless, much less acute than in scabies. 



Eingworm may undergo spontaneous cure in from six weeks to 

 three months. It is more obstinate in calves than in adults, and 

 the want of grooming tends to increase its duration. If it extends 

 over a large part of the body the disease may seriously aftect the 

 animal's health, and the cases described by Macorps prove that where 

 j^ruritus is violent it seriously affects the animal's general condition. 



The patches may finally become confluent and the disease extend 

 over the whole of the neck, shoulder and back, or it may attack the 

 entire body, leaving it practically hairless. 



When the hair has been shed, the crusts and discharge seen at 

 the outset disappear, and the bare spots are covered with a scaly 

 coating, due to excessive production of epidermic cells. 



According to Gerlach, such crusts are thicker where the skin is 

 black, and often exhibit a greyish-white, fibrous, starchy appearance. 

 On unpigmented portions of the skin, which are usually thinner, the 

 crust is less dense, and is slightly yellowish. Gerlach failed to re- 

 inoculate the bare patches of skin left after a primary eruption of 

 ringworm. Where the hair had again grown an eruption could again 

 be j)roduced, though it was usually of a feeble character. 



In a second form of the disease, the spots may be of very small 

 dimensions. The hair falls away, but there is no exudative inflam- 

 mation, and no formation of crusts. In this second form the animals 

 simply show characteristic circular bare spots about the head, neck, 

 or shoulders. 



Causation. The disease is due to the growth of germs on the 

 skin of animals which are in a receptive condition. The parasite 



