THE WONDER OF LIFE 531 



thus lessens the loss, while the ' toning up ' of the muscles 

 increases the supply. Shivering is the attempt of the 

 muscles to ' tone up '. 



It is very interesting to consider some of the exceptions. 

 In the case of many young birds and mammals, a short 

 exposure to cold is fatal, because the thermotaxis or heat- 

 regulating arrangement has not yet been estabhshed. In 

 the egg-laying Mammals — the duckmole and the spiny 

 ant-eater — ^there is an extraordinary range of temperature, 

 which is what one might expect in relative primitive types 

 with a good deal of the reptile about them stiU. In hiber- 

 nating Mammals like the hedgehog and the dormouse, the 

 heat-regulating arrangement has gone out of gear, and the 

 animal becomes colder and colder as the external tem- 

 perature falls. 



But the most famiUar exception — all too famiUar — is 

 fever, which occurs when the fine balancing adjustment 

 has been put out of gear by poisoning, or when the con- 

 ditions of heat-production or heat-loss are such that the 

 normal arrangements cannot cope with them. There may 

 be too much production of heat as in pneumonia, or too 

 Uttle loss as in typhoid. If the temperature of the blood 

 exceed a certain hmit, the nerve-ceUs are fatally injured as 

 in ' sunstroke '. It must be noted, as Professor Eraser 

 Harris points out, that while fever (pyrexia) is the upsetting 

 of thermotaxis, the disturbance of the beautiful thermal 

 balance, it is not now regarded as a wholly bad thing to 

 be reduced at any cost. In a luminous article he says : — 



' Fever is to-day regarded by physicians in a totally 

 different light from what it was even a few years ago — in 

 itself a whoUy bad thing to be reduced at any cost. The 

 increased heat-production is looked on as a reaction on the 



