606 FUNCTIONS OF ANIMALS, 



occasioned by this rapid solution. When the substance is satu- 

 rated with the combustible body, it becomes unfit for supporting 

 combustion, and of course no combustible body will burn in it. 

 This peculiar substance is obviously the oxygen of modern che- 

 mists, which is now known to constitute a fifth part of the volume 

 of common air. 



In 1664, Dr Malachi Thruston, when he took his medical de- 

 gree at Cambridge, defended a thesis entitled De Respirationis 

 usu Primario Diatriba, which he published three or four years 

 afterwards.* He was of opinion that the air, or the purest por- 

 tion of it, was absorbed by the blood in the lungs, and that this 

 portion was necessary to preserve the fluidity and the heat of that 

 liquid. The heat of the body, he says, is owing to the nitrous 

 particles of the air absorbed by the blood, which ferments with 

 the sulphureous particles. He observed that the blood acquir- 

 ed its scarlet colour by its union with air, and says it was with 

 peculiar pleasure that he found that the experiments of Lower 

 agreed with his ideas. Now Lower's work on the heart was pub- 

 lished in 1669. Hence I think we may conclude that Thrus- 

 ton's Diatriba was not given to the public before the year 1669 

 or 1670. 



In 1668, Dr Mayow of Oxford published his Tracts, which 

 have conferred upon him so much posthumous celebrity, after he 

 had languished in obscurity for more than a century. This work 

 consists of five tracts. The first, De Sal-nitro et Spiritu Nitro 

 (Brio, in which he treats of the constitution of air, and gives a 

 theory of combustion very similar to that of Dr Hooke. His se- 

 cond tract, De Respiratione, and his third, De Respiratione Foetus 

 in Utero et Ovo, contain his views respecting that most important 

 function. According to him the nitro-aerial particles (that is 

 the oxygen) of the atmosphere are absorbed by the blood in the 

 lungs. During the circulation, they unite with the salino-sul- 

 phureous particles of the blood. This union is accompanied by 

 fermentation, which evolves animal heat. 



The dark and dusky colour of venous blood is, in his opinion, 

 owing to the salino-sulphureous particles. Fermentation he con- 

 sidered as depending upon the nitro-aBrial particles, and hence he 

 inferred that the motion of the blood was owing to the same 

 source. The chief use of respiration was, in his opinion, to keep 



* It was inserted in the Bibliotheca Anatomica printed in 1685. 



