Theories and Experiments 467 



then inspire only 20 cubic inches, he will have to make 30 respirations 

 per minute to bring the same quantity of oxygen into his body. If 

 he is given air with a half-atmosphere of compression, his lungs will 

 make only 20 respirations, because 20 cubic inches of this compressed 

 air will be equivalent to 30 of ordinary air. 



If the total mass of blood in a healthy man passes through the 

 lungs in 4 minutes and absorbs a certain quantity of oxygen there, 

 in case the lungs are shrunk by disease, it will have to pass through 

 more quickly to absorb the same quantity of oxygen, and for this 

 reason there is a necessary increase in the pulse rate. If compression 

 has made the oxygen content of the air greater in the same volume, 

 the blood will obtain more oxygen from it, and the circulation will not 

 need to be so rapid .... 



An essential action of compressed air is its effect upon the free 

 gases contained in the blood. The presence of these gases permits 

 the mass of the blood to be compressed by the air, so that the vessels 

 contract. This effect at first must be produced particularly upon the 

 vessels on the surface of the body. The capillaries of the skin and the 

 lungs will therefore contract .... 



The increased production of carbonic acid in compressed air needs 

 to be demonstrated by new researches .... 



Since the compression brings more oxygen into the blood, we 

 might expect to see the temperature of the body rise. But that did not 

 take place under observations made with the greatest care .... More- 

 over, the slackening of the respiration and the circulation should 

 compensate for the greater quantity of oxygen contained in the blood. 



A discussion of the perspiration, urine, and nutrition follows, 

 from which no definite conclusion is drawn. 



Tutschek 25 makes a more concise statement of similar opinions. 

 In his opinion, the action of compressed air has two factors: 



The increased mechanical pressure, which modifies the flow of 

 the blood; the increased oxygen content of the blood, which exerts a 

 great influence upon the metabolism. 



We now come to the works of Rudolph von Vivenot. 26 The part 

 describing the changes in the respiratory rhythm as a result of the 

 stay in compressed air has been reported in the preceding chapter. 

 (See page 420.) As to the explanation of the increase in the pul- 

 monary capacity, Vivenot finds it in the following theory: 



Although the increased pressure is exerted equally over all parts 

 of the surface of the body, the effect produced by this pressure is by 

 no means equal everywhere, because of differences in texture, con- 

 sistency, and position of the different organs. 



The pulmonary tissue, which is delicate and elastic and yields 

 easily, will resist the increased pressure less at the base of the lungs, 

 where it rests only on the intestines, which are very compressible, 

 than at the thoracic walls, which are formed of firmer and more com- 



