Within the trabeculae of the sponge-work blood circulates, and between the trabeculae the water passes,.
Small doses of any of them dilate the blood vessels from an action on the vaso-motor centre in the medulla oblongata, as a result of which the heart beats more rapidly and the blood circulates more freely; but larger doses have a general depressing effect upon the circulatory system.
With liquid machines of the compression and absorption system, the rooms are either cooled by means of cold pipes or surfaces placed in them, or by a circulation of air cooled in an apparatus separated from the rooms. The cold pipes may be direct-expansion pipes in which the liquid evaporates, or they may be pipes or walls through which circulates an uncongealable brine previously cooled to the desired temperature.
Quinine hydrochloride circulates in the alkaline blood without precipitation, probably owing to the presence of carbonic acid in the blood.
Thus in parts of California, where high temperatures are liable to prevail during the vintage, the system - first employed in Algeria - of cooling the must during fermentation to the proper temperature by means of a series of pipes in which iced water circulates is now largely employed.