February 26, 1903] 



NATURE 



401 



A 



ANIMAL THERMOSTAT. 1 



THERMOSTAT is an apparatus, or instrument, for auto- 

 matically maintaining a constant temperature in a space, 

 or a piece of solid or fluid matter with varying temperatures in 

 the surrounding matter. 



Where and of what character is the thermostat by which the 

 temperature of the human body is kept at about 98 '4 Fahrenheit ? 

 It has long been known that the source of heat drawn upon by 

 this thermostat is the combination of food with oxygen, when 

 the surrounding temperature is below that of the body. The 

 discovery worked out by Lavoisier, Laplace and Magnus still 

 holds good, that the place of the combination is chiefly in tissues 

 surrounding minute tubes through which blood circulates 

 through all parts of the body, and not mainly in the place 

 where the furnace is stoked by the introduction of food, in the 

 shape of chyle, into the circulation, nor in the lungs where 

 oxygen is absorbed into the blood. It is possible, however, 

 that the controlling mechanism by which the temperature is 

 kept to 98° "4 may be in the central parts, about, or in, the 

 pumping station (the heart) ; but it may seem more probable 

 that it is directly effective in the tissues or small blood-vessels in 

 which the combination of oxygen with food takes place. 



But how does the thermostat act when the surrounding tem- 

 perature is anything above 9S" '4 and the atmosphere saturated 

 with moisture so that perspiration could not evaporate from the 

 surface? If the breath goes out at the temperature of the body 

 and contains carbonic acid, what becomes of the heat of com- 

 bustion of the carbon thus taken from the food ? It seems as if 

 a large surplus of heat must somehow be carried out by the 

 breath : because heat is being conducted in from without across 

 the skin all over the body ; and the food and drink we may 

 suppose to be at the surrounding temperature when taken into 

 the body. 



Much is wanted in the way of experiment and observation to 

 test the average temperature of healthy persons living in a 

 thoroughly moist atmosphere at temperatures considerably above 

 9S°4; and to find how much, if at all, it is above 9S°'4. 

 Experiments might also, safely, I believe, be tried on healthy 

 persons by keeping them for considerable times in baths 

 at 106° Fahr. with surrounding atmosphere at the same tem- 

 perature and thoroughly saturated with vapour of water. The 

 temperature of the mouth (as ordinarily taken in medical 

 practice) should be tested every two minutes or so. The tem- 

 perature and quantity and moisture and carbonic acid of the 

 breath should also be measured as accurately as possible. 



P.S., December 5, 1902. — Since the communication of this 

 note, my attention has been called to a most interesting paper by 

 Dr. Adair Crawford in the Philosophical Transactions for 1 87 1 

 ("Hutton's Abridgments," vol. xv. p. 147), "Experiments on 

 the Power that Animals, when placed in certain circumstances, 

 possess of producing Cold." Dr. Crawford's title expresses 

 perfectly the question to which I desired to call the attention of 

 the British Association ; and, as contributions towards answer- 

 ing it, he describes some very important discoveries by experi- 

 ment in the following passage, which I quote from his paper : — 



" The following experiments were made with a view to deter- 

 mine with greater certainty the causes of the refrigeration in the 

 above instances. To discover whether the cold produced by a 

 living animal placed in air hotter than its body be not greater 

 than what would be produced by an equal mass of inanimate 

 matter, Dr. Crawford took a living and a dead frog, equally 

 moist, and of nearly the same bulk, the former of which was at 

 67°, the latter at 6S", and laid them on flannel in air which had 

 been raised to 106°. In the course of twenty-five minutes, the 

 order of heating was as annexed. 3 



1 By Lord Kelvin. Read before Section A of the British Association, 

 Belfast, 1902. 



- Observations by Governor Ellis in 1758 ; teachings of Dr. Cullen prior 

 to 1765 ; very daring and important experiments by Dr. Fordyce on 

 himself in heated rooms, communicated to the Royal Society of London in 



1774- 



3 In the two following experiments, the thermometers were placed in 

 contact with the skin of the animals under the axillae. — Orig. 



"The thermometer being introduced into the stomach, the 

 internal heat of the animals was found to be the same with that 

 at the surface. Hence it appears that the living frog acquired 

 heat more slowly than the dead one. Its vital powers must 

 therefore have been active in the generation of cold. 



"To determine whether the cold produced in this instance 

 depended solely on the evaporation from the surface, increased 

 by the energy of the vital principle, a living and dead frog were 

 taken at 75 and were immersed in water at 9S , the living frog 

 being placed in such a situation as not to interrupt respiration. 1 



In 



Dead Frog 



85 



8SJ 

 90J 

 91.V 

 91A 

 9li 



Living Frog 



85 

 87 

 89 



NO. 1739, VOL. 67] 



"These experiments prove that living frogs have the faculty 

 of resisting heat, or producing cold, when immersed in warm 

 water ; and the experiments of Dr. Fordyce prove that the human 

 body has the same power in a moist as well as in a dry air ; it 

 is therefore highly probable that this power does not depend 

 solely on evaporation. 



" It may not be improper here to observe that healthy frogs 

 in an atmosphere above 70° keep themselves at a lower tem- 

 perature than the external air, but are warmer internally than at 

 the surface of their bodies ; for when the air was 77°, a frog was 

 found to be 68°, the thermometer being placed in contact with 

 the skin ; but when the thermometer was introduced into the 

 stomach, it rose to 7oV\ It may also be proper to mention that 

 an animal of the same species placed in water at 61° was found 

 to be nearly 6lJ° at the surface, and internally it was 66i°. 

 These observations are meant to extend only to frogs living in 

 air or water at the common temperature of the atmosphere in 

 summer. They do not hold with respect to those animals when 

 plunged suddenly into a warm medium, as in the preceding 

 experiments. 



"To determine whether animals also have the power of 

 producing cold when surrounded with water above the standard 

 of their natural heat, a dog at 102° was immersed in water at 

 114°, the thermometer being closely applied to the skin under 

 the axilla, and so much of his head being uncovered as to allow 

 him a free respiration. 



In 5 minutes the dog was 10S, water 112 



6 

 11 



109, 

 10S, 



112, the respiration having 

 become very rapid. 



,, 13 ,, ,, 108, ,, 112, the respiration being 



still more rapid. 



,, 30 „ „ 109, ,, 112, the animal then in a 



very languid state. 



"Small quantities of blood being drawn from the femoral 

 artery, and from a contiguous vein, the temperature did not 

 seem to be much increased above the natural standard, and the 

 sensible heat of the former appeared to be nearly the same with 

 that of the latter. 



"In this experiment a remarkable change was produced in 

 the appearance of the venous blood ; for it is well known that 

 in the natural state the colour of the venous blood is a dark red, 

 that of the arterial being light and florid ; but after the animal, 

 in the experiment in question, had been immersed in warm 

 water for half an hour, the venous blood assumed very nearly 

 the hue of the arterial, and resembled it so much in appearance 

 that it was difficult to distinguish between them. It is proper 

 to observe that the animal which was the subject of this experi- 

 ment had been previously weakened by losing a considerable 

 quantity of blood a few days before. When the experiment was 

 repeated with dogs which had not suffered a similar evacuation, 

 the change in the colour of the venous blood was more gradual ; 

 but in every instance in which the trial was made, and it was 

 repeated six times, the alteration was so remarkable that the 

 blood which was taken in the warm bath could readily be dis- 

 tinguished from that which had been taken from the same vein 



1 In the above experiment, the water, by the cold frogs and by the 

 agitation which it suffered during their immersion, was reduced nearly to 

 aii*. — Orig. 



