150 RESPIRATION. 



From these facts, it would seem that the most constant effect of alcohol and of alcoholic 

 liquors, such as wines and spirits, is to diminish the exhalation of carbonic acid. This 

 effect is almost instantaneous, when the articles are taken into the stomach fasting ; and 

 when taken with the meals, the increase in carbonic acid which habitually accompanies 

 the process of digestion is materially lessened. Eum, which Dr. Smith found to be a 

 respiratory excitant, is an exception to this rule. Malt liquors seem to increase the ex- 

 halation of carbonic acid. With regard to alcohol itself, Dr. Smith says: "The action 

 of pure alcohol was much more to increase than to lessen the respiratory changes, and 

 sometimes the former effect was well pronounced." 



Kegarding as one of the great sources of carbonic acid the development of this prin- 

 ciple in the tissues, whence it is taken up by the blood, Dr. Smith attributes the grateful 

 and soothing influence of tea, coffee, eau sucree, and the other beverages which he classes 

 as respiratory excitants, to their action in facilitating the removal of this principle from 

 the system. The presence of carbonic acid in the tissues and in the blood produces a 

 sense of malaise, or depression, which we should suppose would be relieved by any thing 

 which facilitates its elimination. It is undoubtedly this indefinite sense of discomfort 

 which induces the act of sighing, by which the air in the lungs is more effectually reno- 

 vated. This view is sustained by the fact that intellectual fatigue and mental emotions 

 diminish the exhalation of carbonic acid. Apjohn cites an instance in which the pro- 

 portion of carbonic acid in the expirations was reduced to 2'9 parts per 100 under the 

 influence of mental depression. 



We have already alluded to the modification in the exhalation of carbonic acid pro- 

 duced by tobacco. 



Influence of Sleep. All who have directed attention to the influence of sleep upon 

 the respiratory products have noted a marked diminution in the exhalation of carbonic 

 acid ; but we again recur to the experiments of Dr. Smith for exact information on this 

 point. Dr. Smith estimated the quantity of carbonic acid exhaled during six hours of 

 sleep, at night, at 4,126 cubic inches. According to this observer, the quantity during 

 the night is to the quantity during the day, in complete repose, as ten is to eighteen. 

 During a light sleep, the exhalation was 10*32, and during profound sleep, 9'52 cubic 

 inches per minute. 



We have alluded to the great diminution in the quantity of oxygen consumed in hiber- 

 nating animals while in a torpid condition. Regnault and Reiset found that a marmot 

 in hibernation consumed only -^ of the oxygen which he used in his active condition. 

 In the same animal they noted an exhalation of carbonic acid equal to but little more 

 than half the weight of oxygen absorbed; so that in this condition the diminution in the 

 exhalation of carbonic acid is proportionately even greater than in the consumption of 

 oxygen. 



Influence of Muscular Activity, Nearly all observers are agreed that there is a con- 

 siderable increase in the exhalation of carbonic acid during and immediately following 

 muscular exercise. In insects, Mr. Newport has found that a greater quantity is some- 

 times exhaled in an hour of violent agitation than in twenty-four hours of repose. In a 

 drone, the exhalation in twenty-four hours was 0'30 of a cubic inch, and during vio- 

 lent muscular exertion the exhalation in one hour was 0-34. Lavoisier recognized the 

 great influence of muscular activity upon the respiratory changes. In treating of the 

 consumption of oxygen, we have quoted his observations on the relative quantities of air 

 vitiated in repose and activity. 



Yierordt, in a number of observations on the human subject, ascertained that moder- 

 ate exercise increased the average quantity of air respired per minute by nearly nineteen 

 cubic inches, and that there was an increase of 1'197 cubic inch per minute in the ab- 

 solute quantity of carbonic acid exhaled. 



The following results of the experiments of Dr. Edward Smith on the influence of 

 exercise are very definite and satisfactory : 



