ANIMAL HEAT 515 



temperature has returned to normal, a fresh puncture may again cause 

 a rise. Injury to various portions of the cortex cerebri in the dog 

 and other animals, and lesions of the pons, medulla oblongata and 

 cord in man may also be followed by increase of temperature. When 

 the spinal cord is cut below the level of the vaso-motor centre the 

 increased loss of heat from the skin due to dilatation of the cutaneous 

 vessels masks any increase of the heat-production which may possibly 

 have taken place, and the internal temperature falls ; but if the loss 

 of heat is diminished by wrapping the animal in cotton-wool the tem- 

 perature may rise. From such phenomena it has been surmised that 

 certain ' centres ' in the brain have to do with the regulation of 

 temperature by controlling the metabolism of the tissues; that they 

 cause increased metabolism when the internal temperature threatens 

 to sink, diminished metabolism when it tends to rise. The cutting 

 off, it is said, of the influence of the ' heat centres ' by section of the 

 paths leading from them allows the metabolism of the tissues to run 

 riot, and the temperature to increase. 



Fever is a pathological process generally caused by the 

 poisonous products of bacteria, and characterized by a rise 

 of temperature above the limit of the daily variation (p. 523). 

 It is further associated with an increase in the rate of the 

 heart and the respiratory movements, often with an increase 

 in the excretion of urea and ammonia in the urine, and -a 

 diminution in the alkalies and carbon dioxide of the blood. 

 It has been suggested that the proximate cause of fever is 

 the action of bacterial poisons or of other substances on the 

 ' heat centres,' and that antipyretics, or drugs which reduce 

 the temperature in fever, do so by restoring the centres to 

 their normal state, by preventing the development of the 

 poisons, aiding their elimination, or antagonizing their action. 

 In favour of this view, it has been stated that when the 

 basal ganglia are cut off, by section of the pons, from their 

 lower nervous connections, fever is no longer produced by 

 injection of cultures of bacteria which readily cause it in 

 an intact animal, while antipyrin has no influence upon the 

 temperature (Sawadowski). But some observers have been 

 unable to find any clear evidence of the existence of l heat 

 centres ' that is, of localized portions of the central nervous 

 system specially concerned in the regulation of the body 

 temperature. And while it is almost certain that some 

 pyrogenic or fever-producing agents cocaine, e.g. act in- 



