202 Historical 



organic liquids placed in a vacuum, and he is led to ascribe to 

 the escape of these bubbles an important part in the symptoms 

 due to decreased pressures: 



When I re.call how our machine (the pneumatic machine) brings 

 out air invisibly held in the pores not only of the water, but also of 

 the blood, serum, bile, urine, and other liquids of the human body; 

 when I reflect that (as I have shown experimentally elsewhere) the 

 pressure of the atmosphere and the elasticity of the air act upon 

 liquids and upon bodies immersed in these liquids, and upon bodies 

 directly exposed to the air, I am inclined to believe that simple 

 changes of the atmosphere from the point of view of weight can, in 

 some cases, have a perceptible influence even on the state of health 

 or sickness of man. When the ambient air, for example, suddenly 

 becomes lighter than before or than usual, the spiritual or airy par- 

 ticles, which are contained in abundance in the blood, naturally will 

 swell this liquid, being able thus to distend the large vessels, and 

 change considerably the speed of the circulation of the blood in the 

 capillary arteries and the veins. That through this alteration several 

 changes can occur in the body will not seem improbable to those who 

 know, in general, how important the rhythm of the circulation of the 

 blood is, although, as to its special effects, I leave them to the specu- 

 lation of the physicians. 



These experiments were repeated, and varied in different ways 

 by all the physicists of this time: Stairs, Derham, Huyghens, 

 Papin, du Hamel, etc. 



I shall quote an extract of the work written in collaboration 

 by Huyghens and Papin; this passage is remarkable for the wholly 

 mechanical explanation given in it of the cause of the death of 

 animals placed in a vacuum in the pneumatic machine. 



According to Huyghens and Papin, 8 warm-blooded animals 

 never revive when they have been placed in a perfect vacuum. 

 They then add: 



M. Guide, who has often dissected these animals which we killed 

 by a vacuum, has observed among other facts that their lungs sink 

 in water, and he maintains that the solidity or density of the lungs 

 of animals which have died thus in a vacuum results from the fact 

 that the blood, carried into the lungs by the arterial vein, presses 

 with such violence upon the bronchi of the tracheal artery, that it 

 forces the air out of them and brings together the walls of these col- 

 lapsed conduits, as if they had been glued together; but, for my part, I 

 do not believe that the blood of the arterial vein can compress the 

 bronchi in this way, because the blood has its own vessels which con- 

 tain it and prevent it from compressing others. . . . 



It is therefore more probable that if the lungs are compressed, 

 it is done by the pleura which can be distended within the chest as 

 the skin is distended on the exterior; but the lungs need not be 



