Theories and Experiments 441 



much rarer than for decreased pressure. The reason is not hard 

 to find; on the one hand, the problem seemed much less interest- 

 ing, since it was not connected with questions of temporary or 

 permanent habitat for man; on the other hand, the necessary in- 

 strumental apparatus is more complicated and more expensive, 

 and the experiments entail some dangers. 



The first author in whom I found theoretical suggestions about 

 the manner in which compressed air should act on living beings is 

 the physician-mathematician Borelli, who, in his celebrated treatise 

 De motu Animalium, 1 sets down the following proposition: 



Prop. CXXV. Probable causes of the suffocation produced in 

 different ways in air which is thick and too much condensed. 



Following the knowledge of his time, Borelli here confuses the 

 effect of compressed air with that of air laden with "ethereal, 

 earthy, aqueous, oily, igneous, saline, etc., particles, as happens in 

 the vapor of coal .... and in the cavern of Lake Agnanus Puteolis." 

 . . . However, he devotes a special section to the effect of "pure air, 

 brought to the highest degree of compression, ut in folle lusorio sit;"' 



I will not deny (he says) that it might be dangerous to breathe, 

 because the extremities near the bronchial tubes and the delicate 

 Malpighian vesicles might be distended and torn by the excessive 

 elasticity, from which dangerous disturbances might result. Moreover, 

 the passage and circulation of the blood would be prevented by it, 

 because the expiration could be made only with great difficulty be- 

 cause of the excessive resistance of the ambient air. (P. 246.) 



Borelli made no experiments. 



It is in the notes which van Musschenbroeck added to the 

 translation of the Memoirs of the Academy del Cimento 2 that we 

 find the first indication of experiments made on animals subjected 

 to the action of compressed air: 



I shall first report (the Dutch physicist says) what happened to 

 animals placed in air much denser than it is at about sea level. M. 

 Stairs shut up a rat in air twice as dense; it lived for five hours; 

 however, after five more hours, it died. But when he had put another 

 rat in air much denser, he observed that it died suddenly. He reports 

 that a fly, in compressed air which made the mercury rise sixty inches 

 above its usual height, was in good condition the third day, and even 

 flew about; but its other companions died. 



M. Derham placed a sparrow in a receiver, in which he com- 

 pressed the air; because it did not hold the air tightly, he repeated the 

 compression from time to time; the sparrow lived for three hours; 

 then, when set at liberty, it seemed to have suffered no harm. Next he 

 put in a titmouse and a sparrow, he compressed the air twice as much; 

 after an hour these birds were as well as when they were put in; then 



