THE HOUSE’S FOOT. 
227 
plienic acid proved very useful with Krause, Gerlach and Zun- 
del. 
After these the best recommended preparations are the salts 
of iron; Hertwig seems to be well pleased with the powder of the 
sulphate, and Arnold recommends the pyrolignite of the same 
metal; Megnin advises specially the perchloride, which, like 
phenic acid, is rather a powerful astringent than a true caustic. 
The preparations of copper have also had their time, and especial¬ 
ly the acetates, such as the oegyptiacum ointment (Girard, Schaack, 
Rainard and Key); the baths of sulphate of copper were em¬ 
ployed by Verrier Jr., of Rouen ; a solution of sulphate of cop¬ 
per and of zinc in water or vinegar were recommended by Delaval 
and Haubner ; Solleysel employed the preparations of copper, 
but added to them arsenic and other drugs; Eichbaum preferred 
the powder of chloride of lime, and Rauch ordinary lime, while 
Aubry employed a mixture of lime and caustic potash. 
Caustics were well recommended by other practitioners, but 
their prescriptions seem to be contrary to the rule we have laid 
down in the beginning. However, one must not forget that the 
tissues of the foot, especially when diseased, offer an extraordinary 
resistance to the action of caustics; they are, so to speak, impen¬ 
etrable, and the irritation they produce remains superficial, while 
where those tissues are healthy such agents produce a deep cau¬ 
terization. Again, this resisting force of the indurated tissues 
against the action of caustics is limited, and it is possible that 
one, two or three applications may apparently remain inefficacious, 
where a fourth or a fifth will give rise to extensive cauterization. 
The result is explained by the repeated irritating influence of the 
caustic agent, which, by gradually increasing the vascularity of 
the parts it touches, increases also the means of their absorption 
and imbibition. These facts must also be present to the practi¬ 
tioner’s mind, and it is by them that he will be guided in their 
use, rendering them at will, simply modifying, catheretic, or deep 
caustics. 
Nitric acid was used by Percivall and Delorme, the latter 
considering it the best means in use. Sulphuric acid has also 
been employed, seldom alone, but mixed with agents likely to re- 
