598 ANNUAL BEPOET SMITHSONIAN INSTITUTION, 1911. 



good reason, they have been generally adopted. In reality, these 

 theories are of two kinds. Just as the engine stops, either from 

 lack of fuel or from an accumulation of ashes, so the organism may 

 plunge into sleep either because the materials necessary for brain 

 activity are exhausted, or because the waste material, generally toxic, 

 is in too great a quantity. 



Among the substances necessary to the working of the nerve cen- 

 ters there are two whose values are now well known, oxygen and chro- 

 matophile. The nerve centers in action consume considerable quan- 

 tities of oxygen, and we may therefore suppose that sleep is due to a 

 lack of sufficient oxygen in the brain, and that it collects in reserve a 

 supply of gas necessary for the coming awakening. This is the theory 

 held by Sommer and Pfluger, relying upon the researches on respi- 

 ratory interchanges made by Pettenkoffer and Voit. The other sub- 

 stance necessary to the building up of the nerve cells, which accumu- 

 lates during sleep, disappearing after prolonged activity, is that which 

 Nissl discovered in nearly all the nerve cells and which is named 

 chromatophile on account of its ability to give color easily. We might 

 therefore explain sleep by the deterioration of chromatophile. That 

 explanation was made by Daddi after having noted the disappearance 

 of chromatophile during a case of prolonged insomnia. 



But though the nerve centers contain substances indispensable to 

 then* working, they also produce during their activity certain waste 

 substances, just as the stove ready to be lighted is full of fuel, then 

 when it is lighted produces ashes that accumulate and diminish the 

 draft. What is the "ashes" of the nervous system ? It is a product 

 of dis assimilation well known for a long time; it is that which leaves 

 the lungs when oxygen enters, the chemical carbon dioxide, commonly 

 called carbonic-acid gas. M. Raphael Dubois has considered it the 

 cause of sleep. To tell the truth, he studied only the hibernal sleep 

 of the marmot, and he concluded that a sleep through an entire winter 

 is the same as daily sleep. We may ask whether this comparison is 

 justifiable. Furthermore, according to M. Dubois, sleep is not a 

 recuperation; we sleep because the carbon dioxide has accumulated 

 in the blood, but, during sleep, the gas continues to accumulate until 

 it is strong enough to excite the nerve centers to wake up. 



Besides the carbon dioxide, there are other less-known wastes from 

 nerve action. These wastes, which have been called "fatigue toxins" 

 (which generate sleep) and which Moliere would certainly have named 

 "dormitive virtues," have also been considered as causes of sleep. 

 Obersteincr thinks that these toxins consist principally of lactic acid ; 

 Preyer believes them easily oxidizable; Bing claims that they act 

 chiefly in preventing oxidation; Errera and Bouchard believe them 

 more or less analogous to the leucomaines ; Lahuson thinks that they 

 are autointoxicating narcotics. But these are merely hypotheses 

 based on experiments as yet insufficient to prove their accuracy. 



