The relation between that part of the whole energy produced which becomes heat and that part of it which becomes work varies enormously according to the kind of work. By comparisons, in regard to this, between static, eccentric, and concentric work, we notice at once that in static muscle work no movement takes place apart from the flow of blood and lymph in the vessels and the "protoplasmic" movements in the cells; all the energy which in ordinary free movements appears in them, in static work becomes heat. The tetanised muscle of a frog becomes heated as much as 0.18° C. (Helmholtz).

With eccentric work we get extremely varying conditions. If, says L. Hermann, I call A the work necessary to hold a weight for a certain time in the hand at the same height, the weight p, the height h, the time t, and the force of gravity ph, the eccentric work, if I allow the weight to sink, = At - ph, the concentric work to raise it again to the same height = At + ph, and the work done to both lower and raise it == At. Similarly, it is clear that in letting the weight sink, not fall, I am able to use all the different quantities of work, even from that which is only the least amount less than the work required to hold the weight at the same height, to that which is the least amount more than no work in letting it fall, without in the least diminishing the speed of its fall. Since in eccentric movement the patient himself does no part of the external movement, and performs less work than he must perform for concentric movement, he develops less heat in eccentric than in concentric movements, other things being equal.

How much of the whole of the energy developed in our ordinary free movements and concentric resistance movements gives rise to heat and how much to movement is not definitely known; it certainly varies considerably. .

0. Weiss considers that movement represents from one-fourth to about one-third of the whole amount of energy. Zuntz considers that in warm-blooded animals one-third of the whole amount of energy is the maximum represented by movement. In frogs, and probably in other cold-blooded animals, this may, according to Danilewsky, stand in the proportion of 1:1

We must, however, remember that a large part of the force which is at first changed to movement is later changed to heat. For example, when the blood arrives at the right auricle there is no longer any of the systolic force of the heart remaining. It has become heat owing to the friction between the blood and the walls of the vessels, and largely owing to the friction in the narrow capillaries; a quantity of heat is produced which altogether, according to L. Hermann, may reach one-ninetieth of the whole amount necessary to the organism. When in walking we use muscle force to lift the trunk, and then Pdf the swinging leg obliquely downwards and forwards on the ground - the foot remaining in its place owing to friction against the ground - and the body falls forward again of its own weight, movement is also changed to heat, to a large extent in merely preventing the fall of the body downwards, and not considering the heat produced by friction between the foot and the ground.

Our greatest task under normal conditions is to replace the loss of heat by radiation and conduction, which two factors we cannot practically distinguish from each other. They take place to a great extent through the skin, and to a less extent through the lungs.

On the whole each separate part of the organism, under normal conditions of the internal organs, is kept at a very slightly varying temperature, which, apart from the usually lower figure in the more peripheral and the slightly higher figure in the more central parts, we are accustomed to state at an average of 37.5° C* In the extremely complicated heat-regulating apparatus of the organism, the highest forces of which belong to the cerebro-spinal nervous system, there remains yet much for us to learn, and I do not propose here to enter into this subject. I will only remind the reader that considerable variations in the expenditure of calories take place according to the temperature of the surrounding air. Johansson has recently demonstrated that the variations which take place normally in the warmth of the body are determined to a large extent by digestion, but first and foremost by muscle work. By vigorous muscle work the temperature of the internal organs may, according to Johansson, rise about 0.5° C. Zuntz noticed (what is to me astonishing) that a quarter of an hour's mountain-climbing in the sunshine produces a temperature in the rectum of 39.5° C. without other unphysiological phenomena. Even if this figure is too high, it seems certain that the increased expenditure of heat- - by quick conduction from the warmed hyperaemic skin, by increased evaporation from the skin, and from the lungs, by increased catabolism, etc. - does not succeed in fully counteracting the increased production.

In order to obtain nutritive equilibrium it is necessary that the output and income of the organism shall be equal. We have already seen the value of protein, fat, and carbohydrate. In order to give an idea of various expenditures in calories I insert here a table of Atwater's showing the expenditure during twenty-four hours for a man weighing 64 kilos.

* In the adult one finds a temperature of 36.7°to37-2°C. in the rectum; in the axilla 0.2° to 0.6° C. less. The skin is usually 32°, in some places 34° to 35° C, but varies considerably. In the internal organs in larger mammals, including man, the temperature is normally as much as 40° C.; it is highest in working muscles and in glands - highest of all in the liver. When taking temperature in the axilla this must be made into an "internal cavity" for fifteen minutes by being closely surrounded by adduction of the arm.

The loss of heat by the lungs is very variously reckoned; Helm-holtz gives it at 70, Rubner at only 35 calories.