take a favourable attitude for the strategy of attack and defence, the preparation above all is by causing him to make movements which raise the temperature of the body. It has always been noticed that the body of an angry man becomes warm, and the phrase "boiling with rage" has passed into common speech. When the anger is not sufficiently violent spontaneously to warm the muscles, the man and the animal make instinctively a series of movements which, while threatening the adversary, tend to increase the vital heat and to raise the body to the degree of temperature most favourable for action. Everyone has noticed that the gestures are more exuberant the less decided the man is to attack. If the anger is really very violent, gestures are useless; the man, in a paroxysm of fury, does not waste his time gesticulating, but throws himself at once on his enemy. His muscles have acquired, merely by the acceleration of the blood-current, the temperature necessary for action.

The gestures of anger are, in reality, violent movements which, in a short time, raise the temperature of the body to the degree at which the muscles act most vigorously. These gestures occur in all animals. They cannot be satisfactorily explained without admitting that they are a preparatory work, the object of which is to give the animal full power of action. The lion which lashes its sides with its tail, the bull tearing the ground with its horns, are doing the same thing as the racehorse in its preliminary canter. When a horse has a little gallop some minutes before the race, the temperature of its muscles is raised a degree; we are heating up a locomotive.

We discover this preparatory working of the muscles in all exercises needing vigour or skill. The pianist plays a few scales or a short prelude before attacking his great piece. In fencing, we make preliminary passes before beginning the assault. In boxing, which needs a great expenditure of force and skill, there is always some preliminary sparring. The object of all these movements is to raise the temperature of the muscles brought

into action. A muscle which has been at work is a warm muscle, and a warm muscle is already in the first stage of contraction, and submits more easily to the action of the will, as the speed already possessed by a moving mass renders more effective a fresh impulse communicated to it.

The effort of a horse which starts a motionless vehicle is always more severe than that required to change its pace from a walk to a trot. The warm muscle is already in a state of semi-contraction, and the will has every facility for increasing and directing its action.

Many phenomena of common occurrences are explained by this action of heat upon muscle. We know that the temperature of the body is lowered during sleep; in hibernating animals which sleep all the winter, the temperature falls from 37° C. to 20° C. Muscular contractility diminishes in the same proportion. By means of registering apparatus, Marey has obtained graphic tracings showing the form and intensity of the muscular contraction in the marmot. He has noted a considerable difference between the moment when the animal has just awakened, and when it is fully awake. The temperature and the muscular energy increase together.

Everyone can notice in himself a certain numbness of the muscles on getting out of bed. Animals surprised in their sleep do not at once recover their muscular energy, and have not at first the swiftness they gain after some seconds' flight. When a hare is put up and has two shots fired at it which do not touch it, the unskilful sportsman almost always thinks it is wounded. It seems unable to run, and its first steps are so slow that a dog could catch it; but after it has gone a few yards the illusions of the inexperienced shot are dispelled; the animal becomes warm and goes like an

arrow.

Heat is then an indispensable element in muscular contraction. But the temperature must not rise too high, for then, instead of increasing the activity of

muscle, heat destroys it. In man and the mammalia, a muscle becomes incapable of contraction at 45° C. At this temperature vital combustions affect the muscular tissues too profoundly, and destroy their properties in a definite manner: the muscle dies.

Excessive muscular work can raise the system to a temperature at which the body can no longer live. This is one of the reasons why a driven animal dies. If the work becomes excessive, so much heat is produced that radiation from the surface of the body and evaporation of the liquids of the economy no longer suffice to keep the temperature at a level compatible with life. The overheated blood poisons the nervecentres; the animal whose body is surcharged with heat owing to too prolonged exercise, dies in a condition similar to that of a man with sunstroke under a tropical sun.

CHAPTER IV.

COMBUSTION.

General Idea of Combustion-Chemical Sources of HeatAncient and Modern Theories-Part played by Oxygen-Oxidation; Hydration; Decomposition-Complexity of the Chemical Phenomena which Produce Heat-Combustible Materials; Food-Stuffs; Reserve-Materials; Tissue-Materials-Results of Combustion-Products of Dissimilation-Products of Incompleted Oxidation; Uric Acid-Elimination of Products of Dissimilation - Eliminating Organs Auto-Intoxication Dangers of Human Miasma.

I.

WORK and heat do not exist independently in the animal machine. Now work goes on incessantly in us. During repose, and even during sleep, the internal organs are never inactive. The heart beats and expends considerable force in propelling the blood through the vessels; the chest rises and falls in respiration; the stomach and intestines perform peristaltic movements to pass the food-stuffs onwards.

The work of the human body continues then night and day; it only ceases with death, and at this moment also is extinguished the fire of animal heat.

Life is impossible without heat.

The heat from which the human machine draws the force necessary for its existence is derived from combustion which goes on inside the organism. In chemistry, the term combustion is applied to the combination of two or more bodies with each other, accompanied by the production of light and heat.

It is evidently a considerable extension of the meaning

of the word combustion, and a somewhat figurative use, to apply it to the phenomena which cause the heating of the body during work. The chemical combination going on in us is not accompanied by the production of light. The phenomena which produce vital heat resemble fermentation rather than combustion properly so called. For example, they rather resemble the changes which go on in a damp hay-stack, than the phenomena we observe in a burning fire.

The sources of vital heat are chemical combinations of infinite variety.

It has been long considered that all the combustions in the system are due to the action of oxygen upon the living tissue. At the present time we fully admit the capital importance of oxygen in the chemical combinations which are the source of work; but we recognize that other bodies take a certain share in the vital actions capable of producing heat; hydrogen for instance.

Further, many chemical reactions which produce heat are accomplished by the simple splitting up of a substance into two others which entered into its composition. In other cases the combination is limited to the hydration of a substance which absorbs some molecules of water, or to its dehydration by loss of these molecules.*

The problem of vital combustion has then become very complicated of late; we may say that it is somewhat perplexed, and that it is difficult to give in a few words a clear and concise summary of it. It is a chapter of physiology which is being re-written, and we cannot at this moment formulate our conclusions.

All that we are able to say is, that the unceasing work of the internal organs, which constitutes life, is the transformation of one force, heat. This force is itself derived from the chemical reactions which set free the heat contained in a latent condition in the molecules of which the organs of the body are made up, and in the foods which serve to nourish the organs.

The chemical reactions which set free and render

Lambling. Sources of Heat and Force.