EFFECT ON THE CIRCULATION 245 



The nitrogen in blood gas analysis is always slightly too much 

 owing to leakage of air during the manipulations. 



The blood can easily be collected if the carotid artery is con- 

 nected with one of the exit tubes of the pressure chamber, for 

 when the tap on this tube is opened the compressed air forces the 

 blood out of the animal's body. 



EFFECT ON THE CIRCULATION 



This can be studied by placing a recording manometer within 

 the pressure chamber, or by observing the capillary circulation in 

 the web of the frog's foot or bat's wing the web or wing being 

 spread over the window of the chamber and illuminated with the 

 arc light. Our observations showed us that compressed air has 

 no mechanical effect on the circulation, and negatived all the 

 mechanical congestion theories of caisson-sickness. 



THE EFFECTS OF DECOMPRESSION 



Out of 24 dogs exposed by Bert to 7-9-J- atm. and then 

 rapidly decompressed in 1-4 minutes, 21 died from the setting 

 free of gas in the blood and tissues 

 and only 1 escaped without symp- 

 toms. The most striking of Bert's 

 results is the following : A dog was 

 put at 9-J- atm. The apparatus 

 burst, the dog instantly died. 

 Enormous subcutaneous emphy- 

 sema was found with gas in 

 stomach, omentum, anterior 



chamber of eye, spinal cord, 



. , J a .,* FIG. 15. Lesion in Spinal Cord 



cerebro - spinal fluid, &C. The O f a Diver, produced by Bubbles of 

 right heart was full of gas, which Nitrogen, set free after rapid decom- 

 pression. The man had dived to a 

 on analysis yielded 15-2 per cent, depth of about 130 ft. (V.Schr otter.) 



C0 2 , 82-8 per cent. N 2 , and 2-0 



per cent. 2 . Similar results have been attained by von Schrotter. 



Having observed the effect of rapid decompression, Bert found 



that dogs may be safely exposed to + 10 atm. if 1-1J hours be 



taken for decompression. The animals must not, of course, be 



