HOW WE KEEP WARM.

Auckland Star, Volume LXI, Issue 229, 27 September 1930, Page 16 (Supplement)

HOW WE KEEP WARM.

ALL A MATTER OF MUSCLE. MEANING OF "TEMPERATURE" WHY WE FEEL COLD. In cold weather it is pleasant to think of the warmth of the body, which physiologists call animal heat. We feel it when we put our cold hands on a cow's neck or when we lift a biggish bird like a duck, writes Professor J. Arthur Thomson in "John O'London's Weekly." To some extent heat is produced by many of the chemical changes that go on in the body, and one of the recent discoveries of Professor A. V. Hill and his fellow-workers is that a demonstrable quantity of heat is given off in a nervous impulse, that is to say in the thrill that passes along a nerve. Thus it is not surprising to find that the most intensely alive of all living creatures, namely the birds, have also the highest temperature. Birds are from 2deg to 14dcg Fahrenheit warmer than mammals; and a fmch on the hedge may be several degrees warmer than man. The cow is one of the warmest of mammals, and some of the bats in summer come a good second to birds. In a general way it may be said that the temperature of a backboned animal is an index to the intensity of the chemical routine or metabolism, but for practical purposes the muscles produce most of the animal heat which is so important in making the vital chemical processes go on quickly and smoothly. Muscles as Engines. When it is very cold we run about, we stamp with our feet, we clap our hands, or we violently strike the sides of our body with our arms; and these common experiences point to the scieutilie conclusion that the muscles are the main producers of animal heat. They have what is called a thermogenic function. It used to be thought that heat is produced by the contraction of the muscle fibres, when they become shorter and broader, and do work. But beat does not seem to be produced in the ordinary actual contraction, a somewhat mysterious physical process, comparable to what happens when a compressed spiral spring is released. But whereas (lie released spring becomes longer, the stimulated muscle becomes shorter. The heat is mainly produced by a combustion (of lactic acid) which enables the muscle to recover itself and go on contracting. In this restitution chemical process there is a production of heat, and carbonic ackl gas is also given off. The Warmth of Sleep. It is plain, however, that the ordinary muscle contractions 011 a big scale, illustrated when we move about, are not necessary for the warmth of the body, for the sleeping baby is producing hca«; though it is lying almost perfectly fjuiet. The blankets, which arc comparable to fur and feathers and fat, are not producing any heat, they are merely lessening the loss that is bound to occur 011 the skin and in the outbreathed air. Muscles continue to produce heat though they are not contracting in the ordinary way. But the broad ' fact is that the living creature is always undergoing combustion; it i 3 like the Burning Bush of old, aflame yet not consumed. Nec tameii consumcbatur. This great fact was first made clcar by Lavoisier, whom the Reds beheaded in 1794, when his genius was at its brightest. He was the first to place the purring cat beside the burning candle, and to show that they were alike in this that both were burning away. He inVcnted a "calorimeter"! Cold-blooded Animals. Backbonelcss animals and the lower backboned animals, namely fishes, amphibians, and reptiles, produce heat, but they have very little capacity for conserving it or for adjusting supply and demand. They always approximate to the temperature of their surroundings, and exceptional cases like the congested beehive are readily explained. But "cold-blooded" doc% not mean that an animal has a low temperature, for this could not be said of lizards basking in the sunshine in warm countries; it means that their body-temperature changes, up or down, according to that of their surroundings. , So this is a case where a technical term is needed to correct the misleading popular one, and the word used is "poikilothermal," which means of changeable temperature. Warm-bloodedness. This quality is restricted to birds and mammals, and it means the power of keeping the temperature of the body constant, day and night, year in and year out. A bird or a mammal may feel cold in winter," but until a certain limit is passed it has the same temperature as it had in summer. It is "stenothermal." The warm-blooded creature can keep its temperaturcaccount balanced from hour to hour, almost from minute to minute. If a bird or -a mammal is losing too much heat from its skin and in its breath, the blood is for the moment slightly chilled. When it flows through a'particular centre in the brain (situated in the corpus striatum of the cerebral region), its slight coldness stimulates the nerve-cells to send out nervous messages which save the situation. Some of these messages command the muscles to produce more heat, while others command a constriction of the superficial blood-vessels in the pale skin, thus reducing the loss. Similarly, if a bird or a mammal or a man is becoming too warm, the heatregulating or "thermotaxic" centre lb affected by the slightly warmed blood, and orders are automatically issued which induce less activity in the muscles, greater activity in the sweat-glands (in mammals), and an expansion of the superficial blood-vessels in the . flushed skin. Thus again "things right themselves and without our knowing anything about it. The evaporation .of the sweat from the mammalian skin helps to keep the body cool; and since birds have no- sweat-glands, it is easy to understand why they often "feel the heat" so badly. Death from Cold. A more or less naked nestling left exposed by some accident to its mother soon takes on the temperature of surroundings, and thus, in the north, quickly dies of cold. The same is true of every young mammal that is born naked. In both cases the heat-regula-tino- centres are not yet in working order. Nature legislates for. the normal, and that includes maternal care. Also [exceptional are the hibernating mjm- ' mals, such as duckmole, dormouse, hcugehog, and bat. For they arc imperfectly warm-blooded creatures that make a strength out of their weakness by becoming winter-sleepers. But that is certainly another story. ..