162 ANIMAL HEAT 



increase of temperature, aids materially in reducing the body 

 temperature. 



Heat Centres. The very many experiments that have been 

 made with the object in view of demonstrating the existence 

 of a special set of heat nerves and heat centres, separate in 

 their action from motor and secretory nerves, are inconclusive. 

 But many significant facts have been brought to light. It 

 has been found that puncture of the brain at the junction 

 of the medulla and the pons causes an increase in heat pro- 

 duction. Section of the cord in the cervical region is followed 

 by a fall in body temperature. These facts have been inter- 

 preted to mean that there exists in the brain anterior to the 

 medulla a general heat centre which constantly keeps in check 

 heat-producing centres located in the cord. Another important 

 fact is shown by the experiment of the "heat puncture" in 

 which a probe, inserted into the corpus striatum of a rabbit 

 causes a rise in temperature which may last for a long time, 

 although the animal shows no other effects from the opera- 

 tion. There is a difference of opinion as to whether the increased 

 production of heat occurs mainly in the liver or in the muscles. 

 Other heat centres have been located in the optic thalamus 

 septum lucidum, cortex, etc. Much work has been done in 

 the hope of throwing light on the causation of fevers. 



Fever. A fever is a pathological process generally caused 

 by the poisonous products of bacteria and which is character- 

 ized by a rise in temperature above the normal. It has been 

 supposed that the action of the bacterial poisons is on the 

 heat centres, and in favor of this view it has been stated that 

 if the basal ganglia are cut off by section of the pons from lower 

 nervous connections fever is no longer produced by injection 

 of bacterial poisons. In conformity with this it is found that 

 antipyrin has no longer any influence on the temperature of 

 the animal. But while it is quite certain that some fever- 

 producing agents (cocaine) act through the central nervous 

 system, it is quite possible that others affect the tissues directly. 

 Likewise, some antipyretics (quinine) act upon heat-forming 

 tissues while others (antipyrin) work indirectly through the 

 nervous system. Fever is always accompanied by other changes 

 than the temperature changes of the body. It is associated 

 with an increased rate of heart beat and respiration. There 

 is a diminution in the alkalies and carbon dioxide of the blood. 



