EFFECT OF LIGHT ON THE ORGANISM. 235 



physiologists, who explain it as the effect of sleep ; but the 

 difference is mainly owing to the presence or absence of 

 sunlight ; for sleep, as sleep, increases, instead of diminish- 

 ing, the amount of carbonic acid expired, and a man sleep- 

 ing will expire more carbonic acid, than if he lies quietly 

 awake under the same conditions of light and temperature ; 

 so that if less is exj)ired during night than during the day, 

 the reason cannot be sleep, but the absence of light.* 



Now, we understand why men are sickly and stunted 

 who live in narrow streets, alleys, and cellars, compared 

 with those who, under similar conditions of poverty and 

 dirt, live in the sunlight. And to give a solid basis to such 

 views, we have Moleschott's striking experiments, which 

 prove that under precisely similar conditions of warmth, 

 age, size, food, &c., the single variation in the condition of 

 light produces an equivalent and constant variation in the 

 amount of carbonic acid expired. In bright sunlight as 

 much as one-fifth more carbonic acid was expired than in 

 feeble light, -f- And have not all farmers and cattle-breeders 

 unconsciously paid tribute to this principle, by keeping 

 their animals in the dark to fatten them ? 



Eeturning from this wide-sweeping excursion to the point 

 from which we started, namely, the love of darkness mani- 

 fested by our animals, the question arises. How can the 

 paradox be reconciled? One might venture on an hypo- 

 thesis, were but the facts a little less refractory : when, 



* MOLESCHOTT, Licht and Lehen, p. 22, citing the experiments of Bocker. 

 t See his Untersuchungen zur Naturlehre des Menschen it, d. Tkiere, i. 12. 

 Also Lis Mhnoire in the Annules des Sciences, 1S56. 



