142 RESPIRATION. 



In the researches on respiration by Dr. Max Pettenkofer, the conditions for accurate 

 observation on the human subject seem to have been fulfilled. Dr. Pettenkofer con- 

 structed a chamber large enough to admit a man and allow perfect freedom of motion, 

 eating, sleeping, etc., into which air could be constantly introduced in definite quantity, 

 and from which the products of respiration were constantly removed and estimated. An 

 incomplete series of observations is published, which has particular reference to the prod- 

 ucts of respiration ; and, thus far, the subject of consumption of oxygen has not been fully 

 considered. This method was adapted to the human subject on a small scale in 1843, by 

 Scharling, but there was no arrangement for estimating the quantity of oxygen furnished. 



Estimates of the absolute quantities of oxygen consumed, or of carbonic acid ex- 

 haled, based on analyses of the inspired and expired air, calculations from the average 

 quantity of air changed with each respiratory act, and the average number of respirations 

 per minute, are by no means so reliable as analyses showing the actual changes in the air, 

 like those of Regnault and Reiset, provided the physiological conditions be fulfilled. 

 When there is so much multiplication and calculation, a very slight and perhaps unavoid- 

 able inaccuracy in the quantities consumed or produced in a single respiration will make 

 an immense error in the estimate for a day or even an hour. Bearing in mind all these 

 sources of error, from the experiments of Valentin and Brunner, Dumas, Regnault and 

 Reiset, and others, a sufficiently-accurate approximation of the proportion of oxygen 

 , consumed by the human subject may be formed. The air, which contains, when inspired, 

 20'81 parts of oxygen per 100, is found on expiration to contain but about 16 parts per 

 100. In other words, the volume of oxygen absorbed in the lungs is five per cent, or -^ 

 of the volume of air inspired. It is interesting and useful to extend this estimate as far 

 as possible to the quantity of oxygen absorbed in a definite time ; for the regulation of 

 the supply of oxygen where many persons are assembled, as in public buildings, hospi- 

 tals, etc., is a question of great practical importance. Assuming that the average respira- 

 tions per minute are eighteen, and that, with each act, twenty cubic inches of air are 

 changed, fifteen cubic feet of oxygen are consumed in the twenty-four hours, which repre- 

 sent three hundred cubic feet of pure air. This is the minimum quantity of air which is 

 actually used, making no allowance for any increase in the intensity of the respiratory 

 processes, which is liable to occur from various causes. To meet all the respiratory exi- 

 gencies of the system, in hospitals, prisons, etc., it has been found necessary to allow at 

 least eight hundred cubic feet of air for each person, unless the situation be such that the 

 air is changed with unusual frequency ; for, beside the actual loss of oxygen in the respired 

 air, constant emanations from both the pulmonary and cutaneous surfaces are taking 

 place, which should be removed. In some institutions as much as twenty-five hundred 

 cubic feet of air is allowed to each person. 



The quantity of oxygen consumed is subject to great variations, depending upon tem- 

 perature, the condition of the digestive system, muscular activity, etc. The following 

 conclusions, the results of the observations of Lavoisier and Se"guin, give at a glance the 

 variations from the above-mentioned causes : 



"1. A man, in repose and fasting, with an external temperature of 90 Fahr., con- 

 sumes 1,465 cubic inches of oxygen per hour. 



"2. A man, in repose and fasting, with an external temperature of 59 Fahr., con- 

 sumes 1,627 cubic inches of oxygen per hour. 



" 3. A man, during digestion, consumes 2,300 cubic inches of oxygen per hour. 



" 4. A man, fasting, while he accomplishes the labor necessary to raise, in fifteen 

 minutes, a weight of 7,343 kil. (about 16 Ib. 3 oz. av.) to the height of 656 feet, consumes 

 3,874 cubic inches of oxygen per hour. 



"5. A man, during digestion, accomplishing the labor necessary to raise, in fifteen 

 minutes, a weight of 7,343 kil. (about 16 Ib. 3 oz. av.) to the height of 700 feet, consumes 

 5,568 cubic inches of oxygen per hour." 



All who have experimented on the influence of temperature upon the consumption of 



