Theories and Experiments 443 



Haller y gave space in his physiology to experimental data and 

 those already revealed by observation of diving bells; he explains 

 them in the following manner: 



If the air is much denser .... the blood, which flows in vessels 

 which are themselves more compressed, undergoes more friction there; 

 this air will inflate the lungs better, and will bring to the left heart 

 the stimulus which will make it contract better .... 



A condensed air is useful and increases the energies of the body. 

 Animals have lived without discomfort in air reduced to a quarter 

 and an eighth of its volume. Under the diving bell, in a denser air, 

 one can live, and a slower respiration is sufficient. A rat lived longer 

 in compressed air than in ordinary air ... . 



Yet there are limits beyond which compressed air is harmful. 

 That happens in the diving bell; in which, when the depth increases, 

 the water enters and compresses the air again. Then respiration is 

 hampered, the belly is compressed, the air enters the auditory meatus 

 painfully, the arms are bound as if with a rope, the membrana 

 tympani is sometimes broken, and blood issues from the ears and the 

 nostrils; finally the heart experiences such resistances that the flow of 

 the blood is almost checked, and some have died thus. A rat died in 

 air reduced to a twentieth of its volume. (P. 194.) 



Experiments similar to those of Stairs, Derham and Musschen- 

 broeck were made at the beginning of this century by Achard, 4 

 who reports them in the following words: 



I have made some experiments on the germination of seeds in 

 compressed air. The result is that the more compressed the air is, 

 the more quickly do the seeds germinate; the difference is considerable. 

 At the same time I made experiments on the length of life of animals 

 in air condensed to different degrees, and I found that in air three 

 times as dense as the atmosphere an animal lives, under circumstances 

 otherwise similar, and in equal volumes of air, five times longer than 

 in atmospheric air. It should be noted that when the air is suddenly 

 compressed to a density about triple, the animal falls into a state of 

 inactivity and lethargic sleep, which apparently is a consequence of 

 the pressure exerted on the brain. After this state has lasted a ldhger 

 or shorter time, the animal regains its natural activity, and then falls 

 into a state of great uneasiness which increases gradually until death. 

 It is also noteworthy that the animal economy feels no ill effect from 

 this state of compression; I have kept birds for an hour in air reduced 

 to one fourth of its volume, and then returned them to the open air; 

 they were in very good condition and showed no sign of inconvenience. 

 (P. 223.) 



Brize-Fradin, after writing the history of diving apparatuses, 

 as we have seen, and after reporting the sensations experienced 

 there, tries to explain these phenomena, and to form a clear idea of 

 the situation in which the man breathing in compressed air is 



