24 Messrs. L. Hill and M. Greenwood. Influence of [Oct. 6, 



Of samples passed immediately after decompression not one yielded less 

 than 1*64 per cent., the mean of 6 being 1*99. 



We are thus led to conclude that, even with a decompression rate of 

 20 minutes per atmosphere, the excess of dissolved nitrogen has not escaped 

 entirely from the tissue fluids, even 15 minutes after decompression. As the 

 matter is of importance, we must examine the validity of our method a little 

 more closely. The accuracy of the analytical process itself was tested by sub- 

 mitting a sample of boiled water to a vacuum in the Hill pump and 

 proceeding exactly as in the urine analyses. No measurable gas was 

 obtained, so that the error due to leakage may be regarded as negligeable. 

 In any case, we disregard analyses in which, owing to the presence of 

 unusually large quantities of oxygen, we can reasonably suspect con- 

 tamination with air. In general, only very small quantities of oxygen 

 were found. 



The admixture of urine that had collected in the bladder while the subject 

 was exposed to a higher pressure would lead to erroneous results, but the 

 complete emptying of the bladder at each observation avoids this source of 

 fallacy. All the urine of the samples passed 15 minutes after decompression 

 must have been separated from the blood after the pressure had fallen to 

 -f- lb., with the exception of the amount present in the tubules and 

 renal pelves, this latter quantity being so small in comparison with the total 

 volume (135 c.c.) passed, that the resultant error can hardly be appreciable. 



That our experiments are not sufficiently numerous to admit of definite 

 statement as to the exact time relations of the process may be granted ; 

 but the qualitative accuracy of the conclusion seems unassailable. 



We have obtained a striking confirmation of our view in the following 

 manner. At the caisson works now being carried out by the London 

 County Council in connection with the new Eotherhithe Tunnel, a positive 

 pressure of 14 — 17 lbs. is employed and only three minutes allowed for 

 decompression.* We have analysed samples obtained from six caisson 

 workers obtained directly after leaving the air lock, with the following result : — 



Nitrogen. 

 If 1-595 



2 1-658 



3 1-506 



4 1-414 



5 1-747 



6 1-744 



* With such low pressures there is little risk in so short a decompression period, 

 t The men had some beer to drink and most of them passed water just before 

 decompression. 



