By the application of cold over the course of an artery, it can be made to contract, and the amount of blood to the district which it supplies may consequently be diminished. This is shown by the accompanying curve taken by Winternitz from the radial artery (Fig. 156).

The first half of the curve (A) was taken before anything had been applied to the arm. The instrument being allowed to remain, ice was next applied to the arm, and the second half of the curve (B) shows the contraction which it had produced in the artery.

When the cold application is allowed to remain for a while, it gradually acquires the temperature of the body, and if evaporation be prevented, it comes to have the same effect as warmth,

Fig.156

Fig.156. - Tracings from the radial artery at the wrist : A before and B after the application of a cloth dipped in cold water round the arm. (After Winternitz.) but if constantly renewed, the contraction of the artery may be kept up. A similar contraction to that just noticed in the vessels of the arm may be produced in the vessels of the head by cold applications around the neck. This is shown by the fall of temperature in the auditory meatus. Cold may be applied to the neck either by a bag containing ice, or by an india-rubber bag, or coils of tubing, through which cold water may be kept constantly flowing.

As a very large proportion of the whole blood in the body flows through the carotids, the application of cold to the neck may act as a general antipyretic. The accurate application of ice-bags to the neck so as to cover the supra-clavicular regions also, and thus to cool the blood in the subclavians, has been recommended in fever, to reduce the temperature generally. In tonsillitis cold to the neck is useful, for its local action.1

Cold to the head is frequently applied in delirium, meningitis, and severe cephalalgia. It may be applied either by a bag containing cold water or ice, or still more conveniently by a cap consisting of india-rubber tubing through which water constantly flows.

A continuous stream of water through an ordinary water-bed reduces the temperature slightly and thus relieves the symptoms in prolonged fever.