CORRESPONDENCE OP RAY. 309 



faction and improvement, finding in it a great many solid 

 observations concerning the respiration of fishes, insects, 

 and other animals. I find that you think that the sub- 

 stance or body of the air passes from the bronchia and 

 lungs into the substance of the blood ; and that, pahidi 

 instar, it foments and maintains the vital flame which you 

 suppose to be in the sulphureous parts of the blood, as the 

 air foments the common flame of a candle, and that the 

 nitre has nothing to do in this effect. 



You and I, sir, agree in this, that the body of the air 

 gets into the mass of blood, and that its nitre there is of 

 no use or energy. We agree, likewise, that the use of 

 respiration is to rarefy and vivify the blood ; we only differ 

 in the manner how this rarefaction is performed. I know 

 that there are very eminent men which are of opinion that 

 the oily parts of the blood do constantly entertain not only 

 a considerable heat, but likewise a true flame in the whole 

 mass : you add to them that the air comes to foment it. 

 I was much of this opinion myself not long ago, but you 

 will be pleased to let me (with submission to your mind) 

 to propose to you, in order to be informed, the difficulties 

 I met with in this opinion. I find that those who eat 

 most of cheese, butter, fat meat, and other sulphureous 

 aliments, and those that are very corpulent and fat them- 

 selves, have generally lesser heat in then' blood, and a 

 slower circulation and pulse, and are less subject to fevers, 

 than persons that are dry and lean, I mean the bilious. 

 I find that in most chemical fermentations sulphur is far 

 from increasing motion and heat, it rather retards it by 

 involving the saline principles, which are the true cause of 

 fermentation and heat. I consider, likewise, that if there 

 was anything of the nature of a flame in the blood, it 

 would only be in the lungs where it meets the air ; but 

 when once it would pass from the lungs into the heart, and 

 into the narrow passages of the veins and arteries, it could 

 no more flame than a lighted candle passed into the deep 

 mouth of a lioUow candlestick. Besides, I cannot believe 

 that the air is an aliment to our common flame, no more 



