OX THERAPEUTICS. 
317 
gutta-percha, or even of dry coverings, upon the saturated 
lint entirely destroys the refrigerant effect, as the dressing 
soon becomes of the same temperature as the part, softening 
the surface, and promoting exhalation from the skin, acting, 
in short, very beneficially under certain conditions, but not 
as a refrigerant at all. In hydropathic practice, the use of 
external coverings is almost constant, and the current ideas 
respecting the effects of cold water, therefore, in many 
instances originate in observations of the action of the fluid 
under such circumstances, when its temperature is very 
considerably elevated. If the douche be employed under the 
hydropathic system, we have of course the primary refrigerant 
action, and the subsequent reaction, as in all cases where cold 
is directly applied. 
The physiological action of refrigerants is easy of demon¬ 
stration ; for example, contraction of the vessels and diminu¬ 
tion of blood in the part are the uniform and invariable 
consequences. If the temperature be sufficiently low, pallor 
and loss of sensation, and even motion, are immediately 
occasioned; under a less degree of cold, the primary impression 
is less marked, and an irregular contraction of vessels may 
cause a quantity of blood to be retained in the veins, producing 
a red or even livid blue colour of the skin. The plan of putting 
a limb into cold water, for the purpose of lessening the 
quantity of blood in the vessels, is perfectly familiar to 
veterinary practitioners, and illustrates very completely the 
action of cold upon the vessels. After a few hours' constant 
application, it often occurs that no blood escapes from divided 
vessels until reaction takes place. 
The return of the blood to the vessels is termed “reaction/' 
and occurs at different,periods after the cold is discontinued; 
if the vessels retain their tonicity, a few minutes only will 
elapse; if the cold has been so intense or so long continued 
as to impair it, reaction may not occur for half an hour; and 
if the vitality of the part is destroyed, it does not happen at 
all; in some instances it is defective, and may require stimula¬ 
tion ; in other cases the return of blood amounts to excessive 
reaction, and necessitates the use of antiphlogistic measures. 
The occurrence of reaction during the operation of cold is 
asserted by the hydropathic schools, but we have not met 
with an instance of it. In the ordinary method of preparing 
a horse for the operation of neurotomy, generally not more 
than two or three hours are required to sufficiently diminish 
the amount of blood in the limb ; but we have known animals 
to stand in water for at least twenty-four hours, and at the 
