92 Mr Dalton's Physiological Investigations on 



animal fat is perhaps the lightest of the components, but even 

 this is heavier specifically than the whole man upon the average. 

 Bone from the leg of a calf I found to be 1.24 specific gravity. 

 The lean of beef (raw) I found 1.045 specific gravity. Blood 

 is from 1.03 to 1.05 specific gravity according to circumstances. 

 On the whole, the solid and liquid parts of the body, examined 

 after life is extinct, would appear on an average to be somewhere 

 about 5 per cent, heavier than water. 



That part of the volume of man which is exclusively occupied 

 by air, and which may therefore be considered as adding nothing 

 materially to the weight of the body, consists of the air-tubes 

 and air-cells of the lungs, the trachea or windpipe, the mouth 

 and other appendages. It is not easy to ascertain the medium 

 volume of air in the lungs of any individual. Messrs Allen and 

 Pepys found the air remaining in the lungs of a man after death 

 somewhat exceeded 100 cubic Inches. I found formerly that 

 after a full inspiration I could blow out 200 cubic inches of air 

 from my lungs, but was then quite exhausted. My ordinary in- 

 spirations and expirations amounted each to about 30 cubic 

 inches *. 



Judging from the above facts and considerations, I should 

 be disposed to conclude that the medium volume of air in the 

 lungs of a middle-sized person would not be less, but rather 

 more, than 100 cubic inches. Besides the lungs there are no 

 other receptacles for air, I beheve, in the body except the sto- 

 mach and bowels, which are occasionally more or less inflated 

 with portions of air either from the atmosphere or other sources. 

 If we allow 150 cubic inches for the volume of air contained in 

 the whole man when entirely immersed in water, it will be as 

 fair an estimate, perhaps, as can be made. But it may be ima- 

 gined by some that the whole substance of the body is pervi- 

 ous to air ; that the skin, the flesh, the blood and even the 

 bones, may be imbued with air, somewhat in the same manner 

 that water is, and yet have no cavities or cells in which the air 

 is collected into a visible volume. Whether such an idea has 

 ever been entertained or discussed I am not aware ; but I pre- 

 sume no one has succeeded in determining either the nature or 

 the quantity of the air so enveloped in the system. We shall 



• Memoirs, vol. ii. (New Series, p. 20.) 



