KNOWLEDGE IN ANCIENT TIMES 17 



ventured to compare the action of the heart to that of 

 a fire or furnace. The air taken to the heart by means 

 of the venal artery (our pulmonary vein) was combined, 

 as he thought, with the blood in the left ventricle to 

 form the animal spirits that were, in his view, such an 

 important feature of the arterial blood. In the process 

 something akin to combustion took place, and heat 

 the animal heat that was the sign of life was given off. 

 This made the heart the hottest organ of the body. Its 

 heat was, however, regulated and controlled, as he thought, 

 by the very agent that fed it. The mechanism for this 

 regulation and control was placed by Galen in the lung. 

 Air entering the lung kept that organ, it was thought, 

 at a low temperature, the superfluous heat being got rid 

 of by the warm breath. The lung was thus enabled to 

 act as a sort of cooling bath to the heart. Respiration, in 

 the Galenic view, thus became a mechanism for regulat- 

 ing the heat of that furnace, the heart. If too little 

 air were taken in, the furnace might be damped down 

 and even put out. If too much air were taken in, the 

 flame was fanned, combustion became fiercer, and the 

 heat increased as in fever. If a great deal too much 

 was taken in, the furnace might be blown out as effec- 

 tively as it might be suffocated by too little air. 



