782 DISEASES or the poll. 



comes greater, and the thickening of the walls progresses, it be- 

 comes obscure. 



In the stable the animal is very quiet, standing with the neck 

 extended and the head carried downward ; he moves with difficulty, 

 without raising the head, and avoiding all movements of the 

 muscles of the neck, and especially of the extensors. At times 

 the distension of the walls of the cyst may be so extreme that 

 the capsular Hgament of the occipito-atloid joint is pushed in- 

 ward in the rachidian canal, and when this occurs nervous symp- 

 toms appear, caused by the pressure of the rachidian bulbs. 



If unremedied, it assumes a chronic condition, with progres- 

 sive distension, which may end in death by pressure upon the 

 bulb. Purulent transformation, and poU evil proper, are also the 

 possible terminations of the atloid hygroma; indeed, it is only in 

 rare instances that it is known to subside by resolution or resorp- 

 tion. In cases of doubtful diagnosis as to the formation of cystic 

 or purulent collections, exploration will relieve the' doubt, and at 

 once settle the question of treatment. 



Blistering and absorbing applications, often repeated, and 

 combined with aspiration, have often reUeved the atloid hygroma. 

 Cauterization in lines or points, both superficial and deep, are 

 also recommended. Injections of tincture of iodine have also 

 their supporters, but they are sometimes liable to give rise to vio- 

 lent irritation, ending in purulent collections, and perhaps necrosis 

 possibly of the cervical ligament. 



F. — Abscess. 



This is the most frequent lesion of the poU, forming at once, 

 when the exciting cause is sufficiently active, or when originating 

 in the manner already described. 



It consists at first, of a diffused, not well defined, swelling of 

 the abundant cellular tissue which separates the muscles of the 

 region, to coalesce at a later period, to form a single purulent 

 gathering, but not until it has macerated and destroyed aU the 

 intermediate tissues into which it had become infiltrated, and this 

 destructive process advances so actively and persistently that when 

 it reaches the surface, instead of closing up, the abscess has be- 

 come transformed into a fistulous center, with a constant dis- 

 charge of mortified, fibrous, elastic, or bony structure. 



