422 THE RESPIRATION 



could be passed through the chamber. The web of the foot was stretched 

 on a wire and fixed so that the small blood-vessels could be seen by apply- 

 ing a microscope to the outside of the window. After carefully observing 

 the circulation of the blood in the vessels at atmospheric pressure, a posi- 

 tive pressure, amounting in some experiments to + 50 atmospheres, was 

 introduced but no effect could be noted on the circulating blood. By 

 opening a tap in the chamber, decompression to zero pressure was quickly 

 effected and, immediately, large bubbles were seen to develop in the 

 blood, blocking the vessels and producing stasis. The bubbles were de- 

 rived from the gas that had gone into solution under pressure. On re- 

 applying the pressure the bubbles of gas again went into solution and 

 the blood circulated normally. When the pressure was subsequently very 

 gradually lowered to zero, the circulation went on undisturbed, and the 

 frog was removed from the chamber in normal condition. 



The process involved in causing caisson disease is evidently the same as 

 that which can be observed in a bottle of aerated water; if the cork in 

 such a bottle is drawn, the dissolved gas escapes as bubbles and effer- 

 vescence results ; if the bottle is recorked, the gas reenters solution and 

 the fluid becomes quiet. If a pin hole is made in the cork, the gas will 

 gradually escape and no effervescence will result. 



Confirmatory results have been secured by observations on mammals. 

 The arterial blood pressure of rabbits was not found to become altered 

 by exposure to compressed air, and various animals placed in a large, 

 strong steel chamber at pressures far in excess of those to which man 

 ever subjects himself did not show any symptoms like those of caisson 

 sickness, unless the pressure was suddenly lowered. Many times also, if 

 symptoms had appeared they could be removed by again subjecting the 

 animals to the compressed air. 



Investigations were also carried out to determine exactly how much 

 gas the blood of an animal subjected to high pressures contains, and how 

 long it takes to absorb the maximal amount of gas and to release it. It 

 was found that the gases that increased in amount were nitrogen and 

 oxygen, and that these become dissolved in the blood according to Dai- 

 ton's law. 



The Prevention of the Symptoms 



The most important practical application of these observations con- 

 cerns the length of time required for the saturation and desaturation to 

 occur, for the results serve as a basis upon which the safe regulation of 

 work in compressed air by man can be conducted. The most significant 

 outcome of the above experiments from this standpoint is that it takes 

 considerable time for the blood to absorb its full quota of gas at a given 



