REGULATING THE HEAT 147 



chapters which deal with the thoracic bellows and the 

 respiratory chambers of the lungs. From olden times, 

 long before Harvey's day, men noticed that the lungs 

 surrounded the heart so as to clothe it — the great com- 

 bustion chamber, so they thought, from which heat and 

 life were distributed to the rest of the body. They knew 

 that the heat of the body always remained about the same, 

 and must therefore be regulated. It was natural for them 

 to believe, when they saw that air entered the lungs and 

 was thus brought in contact with the heart, that breathing 

 and the lungs were Nature's contrivance for regulating 

 the temperature of the body by cooling the heart — the 

 main combustion chamber. We shall see that modern 

 physiologists estimate that only a little over one per cent, 

 of the total heat produced in the body is carried away by 

 the breath. Nevertheless, even up to the time of his 

 death in 1657, Harvey looked upon the lungs as a means 

 of cooling the heart. 



Twenty years spent in dissecting and thinking made 

 Harvey master of the heart's secrets. It took two hundred 

 years of labour by a succession of men to discover the use 

 of the lungs. Their use was eventually discovered not by 

 medical men, but by chemists and natural philosophers. 

 We shall learn many secrets connected with the heat 

 regulation of the body if, for a short space, we follow 

 in the footsteps of the men who, one after the other, 

 succeeded in making discoveries which brought the true 

 use of the lungs into the full light of day. In 1660, 

 when the line of Stuart kings was restored to Britain, 

 and three years after Harvey's death, the Hon. Robert 

 Boyle performed an experiment of a new kind. He 

 placed a lighted candle under an inverted bell-jar, and 

 drawing the air off by means of a newly invented 

 contrivance, the air-pump, showed that the candle went 

 out when the air was exhausted. He replaced the 

 candle by a live mouse ; when the air was extracted the 

 mouse died. Air was thus decisively shown to be 

 necessary to sustain both combustion and life. There 

 was, therefore, a resemblance between combustion and 



