148 RESPIRATION. 



ence connected with the variations with age, which depends upon the condition of the 

 generative system of the female. 



The absolute increase in the evolution of carbonic acid with age, in the female, is 

 arrested at the time of puberty and remains stationary during the entire menstrual 

 period, provided the menstrual flow occur with regularity. During this time, the average 

 exhalation per hour is 714 cubic inches. After the cessation of the menses, the quantity 

 gradually increases, until, at the age of sixty, it amounts to 915 cubic inches per hour. 

 From the age of sixty to eighty-two, the quantity diminishes to 793, and finally to 670 

 cubic inches. 



When the menses are suppressed, there is an increase in the exhalation of carbonic 

 acid, which continues until the flow becomes reestablished. In a case of pregnancy 

 observed by Scharling, the exhalation was increased to about 885 cubic inches. 



Influence of Digestion, Almost all observers agree that the exhalation of carbonic 

 acid is largely increased during digestion. Lavoisier and Seguin found that, in repose 

 and fasting, the quantity exhaled per hour was 1,210 cubic inches, which was raised to 

 1,800 and 1,900 during digestion. Numerous experiments on animals have confirmed 

 this statement. A very interesting series of observations on this point was made by 

 Vierordt upon his own person. Taking his dinner at from 12*30 to 1 P. M., having noted 

 the frequency of the pulse and respirations and the exhalation of carbonic acid at 12, he 

 found, at 2 p. M., the pulse and respirations increased in frequency, the volume of expired 

 air augmented, and that the carbonic acid exhaled had increased from 15*77 to 18'22 cubic 

 inches per minute. In order to ascertain that this variation did not depend upon the 

 time of day independently of the digestive process, he made a comparison at 12 M., at 1 

 and at 2 p. M. without taking food, which showed no notable variation, either in the 

 pulse, number of respirations, volume of expired air, or quantity of carbonic acid exhaled. 

 There can be no doubt that the exhalation of carbonic acid is notably increased during 

 the functional activity of the digestive system. 



The effect? of inanition is to gradually diminish the exhalation of carbonic acid. Bidder 

 and Schmidt noted the daily production of carbonic acid in a cat which was subjected to 

 eighteen days of inanition, at the end of which time it died. The quantity diminished 

 gradually from day to day, until, just before death, it was reduced a little more than one- 

 half. Dr. Smith noted, in his own person, the influence of a fast of twenty-seven hours. 

 There was a marked diminution in the quantity of air respired, in the quantity of vapor 

 exhaled, in the number of respirations, and in the rapidity of the pulse. The exhalation 

 of carbonic acid was diminished one-fourth. An interesting point in this observation was 

 the fact that the quantity was as small four and a half hours after eating as at the end 

 of the twenty-seven hours. " An increase of carbonic acid in the absence of food, at or 

 near the period when it is usually increased by food," was also noted in the experiment 

 by Dr. Smith. 



Influence of Diet. Eegnault and Reiset, in their experiments on animals, studied the 

 effect of different kinds of diet upon the relations of the quantity of oxygen absorbed to 

 the carbonic acid exhaled. About the only conclusive and extended series of investiga- 

 tions on the influence of diet upon the absolute quantity of carbonic acid exhaled are 

 those of Dr. Smith. This observer made a large number of experiments on the influence 

 of various kinds of food and extended his inquiries into the influence of certain beverages, 

 such as tea, coffee, cocoa, malt and fermented liquors. We have already fully described 

 the method employed in these experiments, and the conclusions, which are of great 

 interest and importance, are very exact and reliable. 



Dr. Smith divides food into two classes, one which increases the exhalation of carbonic 

 acid, which he calls respiratory excitants, and the other, which diminishes the exhalation, 

 he calls non-exciters. 



The following are the results of a large number of carefully-conducted observations 

 upon four persons : 



