THE CHEMISTRY OF SLEEP. 239 



We have seen that during natural sleep the carbon dioxide 

 expired (during wakefulness between three and four volumes 

 per hundred of air from the lungs) diminishes as the circulation 

 diminishes. Many claim that a succession of rapid but long- 

 drawn respirations will quickly bring on drowsiness, and often 

 sleep even ensues. This can be attributed only to a small over- 

 charging of the circulation with carbonic acid. It must be re- 

 called also that carbonic-acid waters and effervescent drinks gen- 

 erally produce with many a decided though transient sedative 

 effect. But in this way doubtless none of the gas reaches the 

 blood, except the little thrown off from the stomach by eructa- 

 tion, this being incidentally and partially inhaled. The gases 

 contained in arterial and venous blood appear to vary somewhat. 

 Several authorities agree, however, that the amount of free car- 

 bonic acid in arterial is much smaller than in venous blood, 

 while the oxygen in the former (combined mainly with the 

 hsemoglobin) is much larger. Pfliiger made the free carbon 

 dioxide, mostly in solution, in red arterial blood of a dog thirty- 

 four volumes and a half per hundred, while in the blue venous 

 blood it rose as high as fifty, or half the volume of the blood. 



The generalization referred to is simply that normal sleep and 

 sleepiness, or drowsiness, are due to a small increase over the aver- 

 age of the carbonic acid in solution in the blood, arising through its 

 overproduction from the greater amount of muscular and other 

 tissue that undergoes oxidation during the waking hours. Dur- 

 ing the sleeping hours this overload of the anaesthetic gas is grad- 

 ually discharged until wakefulness results. 



In this brief discussion no room has been occupied with what 

 are called hypnotism, clairvoyance, trance, mind-reading, etc. 

 These are outside of our scope being, if authentic, not natural 

 but supernatural phenomena, pertaining to the realms not of 

 law but of miracle. 



Experiments, coutinued tlirongh many years, by Dr. S. Rideal, show that the 

 chemical activity of sunlight during winter on the high Alps is much greater than 

 at lower levels, and enormously greater than in large towns at the same season. 

 This increased activity may contribute importantly to the beneficial effects of- 

 health of residence in such regions. 



Haldane discussed the subject of the fatality to miners of " after-damp," hitherto believed 

 to owe its effects to carbon dioxide. He shows that absence of oxygen is the real cause of 

 death in these cases. He introduces the novel and highly rational suggestion that all parts 

 of mines should be provided with reservoirs of highly compressed oxygen. A pint of this, 

 he shows, would keep a man alive for an hour. Doubtless, with our present means and 

 knowledge, oxygen could be stored in mines and elsewhere, in its liquefied form, for this 

 and other valuable uses. H. W. 



