600 OPEEATIONS ON THE FOOT. 



phyton or parasitic plant of the horn, by analogy with the tricho- 

 phyton, the parasite of the hair. We consider this name very 

 appropriate and prefer it to the name of odium batracosis, parasite 

 of the canker, which Mr. Megnin has also proposed. 



Etiology. — The causes of canker are yet but little known; 

 there is one, however, which cannot be ignored, and which, if it 

 does not produce the disease, assists materially in its develop- 

 ment and is iadispensable to its existence. We refer to the con- 

 dition of dampness. It is that influence of dampness which 

 explains why the disease is so very common ia the marshy lands of 

 Poitou ; in the pastures of Holland, and in general in low grounds ; 

 and why it is more frequent ia northern than in southern coun- 

 tries. Canker is incomparably more frequent in raiay seasons than 

 in those where dryness predominates. We have already seen in 

 the history of the disease that it is since the streets and the stables 

 of administration are kept more free from dampness that canker 

 has become less common. 



Sometimes the action of direct irritating causes has been 

 admitted, and then the canker has been attributed to irritating 

 muds and the excrementitial liquids of stables ; their contact often 

 giving rise upon the skin, upon the glomes of the frog, to an ery- 

 thematous inflanxmation, soon followed by a serous flow, which ex- 

 tends to the sub-horny structures and gives rise to an exudation 

 in the lamiaae of the frog. This cause produces the rotten frog 

 (thrushes) but not canker. We beheve that this cause has princi- 

 pally been admitted by veterinarians who look upon thrushes as 

 the first stages of canker, but this is not so, and for canker to 

 develop itself under similar conditions, others are necessary, which 

 are as yet unknown. 



Canker has also been attributed to narrow and contracted feet, 

 so common ia horses of meridional climates, and in which the sole 

 is very concave, with the frog and pyramidal body shrunk in. 

 Often ia the lamiase of these feet a sero-purulent moisture is dis- 

 covered, more or less offensive, which is a rotten frog, but not 

 canker, and but seldom followed by it. 



To produce canker a simple irritation of the sub-homy struct- 

 ure is not sufficient. There must be a special cause, proper to 

 canker, stimulatiag alone the characteristic changes of the cause. 

 This cause we find in the cryptogam which characterizes canker, 

 propagates it, and which has no power of spontaneous existence. 



