An increased production of heat is obvious under conditions of climate demanding prolonged exposure to low temperature. An abundantly fatty diet promotes the formation of heat, while suitable clothing checks its dissipation. Although it is claimed by Liebermeister that sudden exposure to cold stimulates heat-production, Rosenthal[6] disputes this {39} statement, and maintains that it is still to be regarded as doubtful whether the production of heat can be varied to suit the demands of sudden and temporary changes of temperature. With the admission of this doubt, the regulation of the temperature of the body, under the circumstances just referred to, is mainly accomplished through the influence of agencies favoring or checking the loss of heat. Since heat is largely brought to the surfaces of the body by the circulating blood, modifications in the fulness and rapidity of this superficial current produce corresponding differences in the amount of heat and moisture presented. Such variations are considered to be accomplished through the action of the vaso-motor nervous system, whose differing effects are apparent in the pale, cool skin and the flushed, warm surface. [Footnote 6: _Op. cit._, 413.] The search for the regulation of such vaso-motor action has led to the view that the production of heat, as well as its dissipation, may be influenced from a nervous centre. Wood[7] claims that the result of experiments made by him proves the existence of such a heat-centre in or above the pons. Although admitting the possibility of its being a muscular vaso-motor centre, he regards it rather as an inhibitory heat-centre, which acts, as suggested by Tscheschichin, by repressing the chemical changes in the constituents of the body through which heat is produced. [Footnote 7: _Op. cit._, 254.] This view is objected to by Rosenthal,[8] on the ground that the facts are not universally agreed upon, and their interpretation is somewhat vague. Even the increased production of heat as determined by Wood, if admitted, may be regarded as the result of a modified circulation. [Footnote 8: _Op. cit._, 442.] The preservation of a normal range of temperature in general is to be recognized as the result of variations in the relation of heat-production to heat-dissipation. The causes which influence this relation may act from without or from within, and are regarded as producing their effect by means of the vaso-motor nervous system. The causes which act from within are those concerned in the febrile elevation of temperature. Whether the latter is associated with, or independent of, inflammatory processes, the question of first importance relates to the modification of physiological conditions. The causes of the physiological production of heat and its dissipation have already been referred to, and the same elements demand consideration in the pathological range of temperature so striking in fever.