1906.] Influence of Increased Barometric Pressure on Man. 453 



tions; so far as it goes, however, it is in favour of such an inference. 

 Summing up the results of the present investigation : — 

 It is proved that — 



(1) A man can be submitted to a total pressure of seven atmospheres 

 without untoward effects, provided decompression be affected gradually, and 

 the capillary circulation be aided by repeated contractions of muscles, joint 

 movements, and charges of posture. 



(2) We have no sense of increased barometric pressure so long as the 

 former is constant. 



It is probable — 



(1) That the subjective effects of increased pressure, apart from voice 

 changes and lip amesthesia; depend upon psychical conditions such as 

 anxiety and excitement. 



(2) The changes in the percentage of carbon dioxide in the alveolar air 

 are conditioned solely by physical variations, and not by any increase or 

 diminution in the respiratory metabolism. 



In conclusion we would remark that we are unable to find any evidence 

 in support of Snell's (15) opinion, that the presence of CO2 in the respired 

 air exercises a peculiarly unfavourable influence under increased pressure. 

 Thus in one experiment the percentage of C0 2 in the chamber air, at 

 + 31 lbs. was - 62 (equivalent to over 1-8 per cent, at + 0), and no 

 untoward results occurred on decompression. 



These researches were carried out with the aid of a grant from the Royal 

 Society Government Grant. 



REFERENCES. 



1. Paul Bert. 1 La Pression barom£trique.' Paris, Masson et Cie., 1878. 



2. Heller Mager and v. Schrotter. ' Luftdruck-Erkrankimgen mit besonderer Beriick- 



sichtigung der sogenannten Caisson-Krankheit.' Wien, 1900 ; also v. Schrotter, 

 ' Der Sauerstoff in der Prophylaxe und Therapie, : etc. Berlin, Hirschwald, 1904. 



3. Hill and Macleod. ' Journal of Physiology,' vol. 29 (1903), No. 6. 



4. ' Journal of Hygiene,' vol. 3, No. 4 ; ' Roy. Soc. Proc.,' vol. 70, p. 455. 



5. Hill and Ham, ' Physiol. Soc. Proc.,' July 1, 1905, p. vi. 



6. Heller Mager and v. Schrotter. Op. cit., pp. 474, et seq. 



7. H. Hersent. 'Note sur l'Emploi de 1' Air comprime pour l'Execution des Ouvrages 



hydrauliques, et sp6cialement des Fondations.' Paris, Iniprimerie Chaux, 1895. 



8. Op. cit., p. 34. 



9. Op. cit., p. 21. 



10. Lorrain Smith. " Pathological Effects due to increased Oxygen Tension," ' Journal 



of Physiology,' vol. 24, p. 19 (1899). 



11. Heller Mager and v. Schrotter. Op. cit., p. 624. 



12. Op. cit., p. 653. 



13. Op. cit., p. 524 and Plate III. 



14. Haldane and Priestley. ' Journal of Physiology,' May, 1905. 



15. Snell. 'Compressed Air Illness, or so-called Caisson Disease.' London, 1896, Lewis, 



p. 212. 



