358 



KNOWLEDGE. 



September, 1910. 



things as animals of constant temperature (warm- 

 blooded). The solution to the puzzle is the high 

 development of the nervous system in animals 

 known as homoiothermic. In a mammal AA'hen 

 the temperature falls, the lirst result is loss of 

 heat from the skin and an incipient depression of the 

 temperature, but, through the nerves of the skin, 

 impulses are sent into the nervous system which 

 emerge as reflex stimuli to cause contraction of the 

 skin vessels and increased heat-i)roduction in the 

 muscles. The constriction of the skin \essels shuts 

 some blood out of the skin and so diminishes heat- 

 loss, while the increased tone of the muscles increases 

 heat-production, and thus the loss of heat due to the 

 fall of temperature is so rapidly compensated for that 

 the temperature does not hnalh tall. Shivering is 

 the familiar reflex effort on the part of the nniscles to 

 increase their heat as a result of the superficial heat- 

 loss. 



This power of balancing thermogenesis against 

 thermolysis we call thermotaxis : the homoiothermic 

 animals have, \\hile the poikilothermic animals have 

 not, the power of thermotaxis. Now fever (pyrexia) 

 is the upsetting of thermotaxis, the disturbance of 

 this beautiful thermic balance. Theoreticallw fe\'er, 

 or a rise of temperature. ma\' occur it the heat- 

 production is too rapid for the heat-loss, or on the 

 other hand the heat-production being unaltered, if the 

 heat-loss is dimished in rate. Both these states of the 

 upset thermal balance occur. Dr. Hale White, the 

 London physiologist, has shown that whereas in 

 pneumonia and erysipelas the fever is due to increased 

 thermogenesis, in typhoid fever and in supiuiration 

 the rise of temperature is due to a diminutimi in the 

 thermolysis. Fever is to-da}- regarded In- physicians 

 in a totally different light from what it was even a few 

 years ago — in itself a whollv bad thing to be reduced 

 at any cost. The increased heat-production is looked 

 on as a reaction on the jiart of the li\-ing cells to the 

 noxious stimulus of the micro-organism or its soluble 

 poison, a response of a protective nature rather than 

 of any other kind. Hence the indiscriminate lowering 

 oi the temperature by drugs (antipyretics) is not now 

 nearly so common as it used to be. It is recognised 

 as possible that the increase of heat (fever) may be 

 evidence of sufficient vitality on the part of the living 

 protoplasm to withstand the assaults of the infective 

 agents, the increased heat being the bio-ph\-sical 

 response to the micro-organic insults. The tlrugs 

 which benefit fever most are now regarded as doing 

 so, not because they lower the temperature, but 

 because they attack the specific cause of the 

 malady ; quinine, for instance, in malaria destroying 

 the parasitic plasmodium malariae, the salicylates 

 antagonising the mate-.i'-s morbi of rheumatic fever. 

 Those versed in vegetable physiology have been able 

 to show that even in the case of parasites attacking 

 trees there is a rise of temperature as a reaction to 

 these assaults ; and therefiTe botanists actualh- 

 speak of " fever "' in plants. 



Of course it is not to be imagined that under no 

 circumstances is fever, or ver\- hot blood, injurious to 



the l)od\-. W'ithin the last few years definite experi- 

 ments have been made showing that blood hotter 

 than a certain temperature does permanentl}- damage 

 the cells of the central nervous system. A short 

 exposure to 47° C, or a longer one to 42° C, killed 

 the cells of an animal's brain hx coagulating one of 

 the essential constituents of their living substance. 

 " Sunstroke," as it is called, is the result of the too 

 hot blood injuring the cells of the brain, and especially 

 those related to consciousness. W'hen the cells are 

 only slightly injured the person may recover, and be 

 " a little queer in the head " for the rest of his life ; 

 if. h()we\er, the cells are decidedh' over-heated, as in 

 " heat-stroke " or "heat-apoplexy," death in collapse 

 superx'enes, the person ne\'er regaining consciousness. 

 Heat-stroke of this kind ma)- occur in places to 

 which the sun never gains access, as, for instance, 

 in front of the furnaces of a steamer in the Red Sea. 

 On the other hand, depression of the temperature 

 of the blood below its normal is as fatal, although not 

 so rapi(ll\-, and tor quite other reasons. Great loss 

 of heat depresses the tissues so that death results. 

 What is kno\\-n to Coroners" juries as " death from 

 exposure " is really death due to heat-loss. An 

 underfed, poorl\- clothed, and [>erhaps also alcohol- 

 intoxicated person falls asleep out-of-doors on a 

 frosty night ; so much heat is lost that the heart and 

 nervous system ne\'er recover : the person never 

 wakes. The lowest (subnormal) temperatures in man 

 ha\-e been recorded imder these conditions (about 

 NO" F). 



The fact of the constancy of the temperature of 

 the blood was recognised in the graduating of the 

 thermometer. Very earl\- in the e\-olution of that 

 simple but indisi)ensable instrument, an upper and a 

 lower fixed jxiint had to be agreed on. The lower 

 point was \-irtuall\- fixed in 1665 when Hooke 

 advised that the temperature of water ii-i the act 

 of freezing should be accepted as the zero. Halle\-, 

 the astronomer, was one of the first to assert that 

 the ten-iperature of boiling water was alwax's the 

 same, and thus a second fixed point was got. It is 

 believed that the suggestion that the temperature ot 

 the blood or " blood-heat " n-iight be a convenient 

 fixed point was made by no less a man than Sir 

 Isaac Newton in 1701. The temperature of the arm- 

 pit of a health\- man, Newton proposed to call twelve 

 degrees, the ten-ipierature of freezing water being zero. 

 Fahrenheit in 1714 ailopted this suggestioi-i and took 

 the body temperature as a fixed point, but his scale 

 had 180 degrees in it, for it ranged from —90'^ (tem- 

 perature of a mixture of ice and salt) to +90 ', which 

 was blood-heat. Acting on the suggestion of the 

 Danish astronomer Roemer, Fahrenheit call his zero 

 (which he thought absolute zero) 0°, and blood- 

 heat 24°, a duodecimal not a decimal scale. Later 

 he liecame dissatisfied with the largeness of the 

 degrees, and therefore subdivided each into four : 

 twent-\'-four thus became ninet\'-six, which accounts 

 for a figure of this order standing for the temperature 

 of the blood, a fact which very few- people could 

 satisfactorih- explain. 



