the Atmospherical Pressure on the Animcd Frame. 93 



' now examine how far such a notion is countenanced by the pre- 

 ceding statement of facts. 



According to the preceding table of Robertson, the average 

 bulk of the ten men was 2.618 cubic feet, 4.500 cubic inches 

 nearly ; but of this volume 150 inches according to the above 

 estimate were air, and the remainder 4350 inches were solid and 

 liquid parts of the body. Now the average specific gravity of 

 those parts of the body has been estimated above at 1 .05 when 

 examined as dead matter : this would make their weight equal 

 to 4567 cubic inches of water ; whereas it was found by actual 

 weighing, to be 146 lbs. as per table, = 4044 cubic inches : hence 

 the observed weight was less than the calculated weight, a por- 

 tion equal to the weight of 523 cubic inches of water, or more 

 than one-ninth of the whole weight of the body. 



Here is a discrepance that demands an investigation. Can 

 Robertson's table of the specific gravities of men give too low 

 an estimate ? This is not likely ; every one knows that the 

 human subject generally floats in water till the lungs become 

 filled with that element, — a proof that the body is lighter than 

 water ; and many persons are observed to swim with the whole 

 head constantly above the surface of the water. 



Have we overrated the specific gravities of the component 

 parts of the body ? I think not : bones, and flesh, and blood 

 are certainly all heavier than water, some more, some less. 



Has the capacity of the lungs for air been underrated.'^ I 

 cannot imagine that any one will contend that the lungs of a 

 middle-sized man will hold, at a medium state of inflation, six 

 times the volume of air we have assigned. Upon the whole, I am 

 inclined to believe the true explanation of the difficulty will be 

 found in this, that the substance of the body is pervious to air, 

 and that a considerable portion of it constantly exists in the 

 body during life, subject to increase and diminution according 

 to the pressure of the atmosphere ; in the same manner as it 

 exists in water : and, further, that when life is extinct, this air 

 in some degree escapes and renders the parts specifically heavier 

 than when the vital functions were in a state of activity. 



The facts that water absorbs air of all kinds, that the quan- 

 tity of the air absorbed is proportioned to the pressure and den- 

 sity of the gas, whether it be alone or mixed with othtr gases, 



