186 
A. ZUNOEL. 
development and is indispensable to its existence. We refer to 
the condition of dampness. It is that influence of dampness 
which explains why the disease is so very common in the marshy 
lands of Poitou ; in the pastures of Holland, and in general in 
low grounds ; and why it is more frequent in northern than in 
southern countries. Canker is incomparably more frequent in 
rainy 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 ad¬ 
mitted, and then the canker has been attributed to irritating 
muds and the excrementitial liquids of stables; their contact of¬ 
ten giving rise upon the skin, upon the glomes of the frog, to an 
erythematous inflammation, soon followed by a serous flow, 
which extends to the sub-horny structures and gives rise to an ex¬ 
udation in the laminae of the frog. This cause produces the rot¬ 
ten frog (thrushes) but not canker. We believe that this cause 
has principally been admitted by veterinarians who look upon 
thrushes as the first stage 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 in horses of meridional climates, and in which 
the sole is very concave with the frog and pyramidal body shrunk 
in. Often in the laminae of these feet a sero-purulent moisture is 
discovered 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-horny 
structure is not sufficient. There must be a special cause, proper 
to canker, stimulating alone the characteristic changes of the 
cause. This cause we find in the cryptogam which characterizes 
canker, propagates it, and which, like other living beings, has no 
power of spontaneous existence. 
As with other parasitic diseases, canker is communicable by 
contagion ; although the examples are quite rare, they cannot be 
doubted. Hurtrel, d’Arbova], PJa-ss, Blind and Megnin have 
