I9I2] Lafayette B. Mendel 147 



available, although still far from complete, suggests that these pul- 

 monary activities are indirectly but powerfiilly influenced through 

 conditions affecting the skin, and that it is in this manner that Venti- 

 lation influences health. 



The hygienic physiology of work in compressed air 



J. J. R. MACLEOD 



Although it is now a well-established fact that the Symptoms of 

 Caisson disease and diver's palsy are due to the sudden liberation o£ 

 bubbles of nitrogen in the blood and tissue fluids, on account of too 

 sudden decompression, there are several peculiarities regarding the 

 conditions which influence the safety of decompression about which 

 there is still a certain degree of uncertainty. This is the case more 

 particularly with regard to : ( i ) Whether the decompression should 

 be uniform or in stages; (2) how long it should take in proportion 

 to the time of the shift and the pressure employed; (3) the degree 

 to which the breathing of oxygen increases the safety of decompres- 

 sion. Although, as insisted on by Haidane and others, it is no 

 doubt the case that " the absolute air pressure can always be reduced 

 to half the absolute pressure at which the tissues are saturated 

 without risk " yet, in practice, it has not been found that the method 

 is in any way superior to that of gradual decompression. 



The time that should be taken in decompression depends on the 

 length of the shift in the caisson, because the Saturation of the re- 

 moter parts of the body with nitrogen continues for a long time 

 after this has been attained in the blood and the more accessible tis- 

 sues. Tables indicating what time should be allowed have been 

 prepared by Haidane and by Japp. 



The advantages of breathing oxygen are not only that it accel- 

 erates the diffusion of nitrogen out of the lungs and, therefore, out 

 of the blood; but, if Symptoms have already appeared, it supplies 

 enough oxygen to keep life going when the circulation is danger- 

 ously obstructed by nitrogen bubbles. In using oxygen at higher 

 pressures, its toxic action must however be kept in mind. 



Recompression, either by placing the caisson worker in a pres- 

 sure Chamber or by having the diver descend again to a certain depth 



