ANIMAL HEAT 599 



muscular work, which increases the metabolism more than 

 high fever, only causes in a healthy man a rise of about i C. 

 in the rectal temperature. When the work is over, the tempera- 

 ture comes rapidly back to normal. The essence of the change 

 in fever is a derangement of the mechanism by which in the healthy 

 body excess or defect of average metabolism, or of average heat- 

 loss, is at once compensated and the equilibrium of temperature 

 maintained. 



This derangement only lasts as long as the temperature is 

 rising. When it becomes stationary at its maximum we have 

 again adjustment, again equality of production and escape of 

 heat ; but the adjustment is now pitched for a higher scale of 

 temperature. A rough analogy, so far as one part of the pro- 

 cess is concerned, may be found in the behaviour of the ordinary 

 gas-regulator of a water-bath. It can be ' set ' for any tempera- 

 ture. That temperature, once reached, remains constant within 

 narrow limits of oscillation ; but the regulator can be equally 

 well adjusted for a higher or a lower temperature. It is, how- 

 ever, important to note that the equilibrium is more unstable in 

 fever than in health, so that changes of external temperature 

 more easily depress or increase the temperature of a fever patient 

 than of a healthy man. 



Rosenthal has concluded from calorimetric observations that, 

 in the first stage of fever, while the temperature is rising, there 

 is always increased retention of heat. Maragliano actually 

 found evidence, by means of the plethysmograph, that the 

 cutaneous vessels are at this stage constricted, and that the 

 constriction may even precede the rise of temperature. Both 

 observations lend support to the famous ' retention ' theory of 

 Traube. In the great majority of cases the production of heat 

 is also increased, on the average by 20 to 30 per cent, of the 

 normal production of a resting man. The increase ^may be 

 much greater during the chill which ushers in so many infections 

 on account of the muscular contractions in shivering. During 

 the period of rising temperature the production of heat is not 

 necessarily increased. At the height of the fever there is often, 

 though apparently not always, an increase in the heat-production. 

 After the crisis, while the fever is subsiding, the rate at which 

 heat is being lost rises sharply. As to the explanation of the 

 increase of metabolism in fever, and especially of the increased 

 metabolism of tissue-protein, various views have been held. 

 Some have gone so far as to say that the increase is merely the 

 consequence, not the cause, of the rise of temperature. But the 

 rebutting evidence which has been brought against this view is 

 strong and, indeed, overwhelming. It is perfectly true that, 

 when the temperature of the body is artificially raised by pre- 



