392 OF RESPIRATION. 



in the maintenance of the respiration) ; and partly in the diminution in the 

 dissipation of the heat of the body itself. 



IX. Period of the Day. Independently of these variations, which have 

 their source in the condition of the individual, there is reason to believe 

 that there is a diurnal cycle of change in the quantity of Carbonic acid ex- 

 haled; the maximum being (cccteris paribus) before and after noon, and the 

 minimum before and after midnight. From the experiments of Scharliug 

 upon the Human subject, it would appear that the average proportion ex- 

 haled by day to that exhaled by night is as 1| to 1 ; and this difference does 

 not seem to be affected by sleep or wakefuluess. Dr. Ed. Smith found that 

 the quantity of Carbonic acid varied at every moment; and that there were 

 similar hourly variations in the quantity of Carbonic acid evolved, as in the 

 rate of pulsations to which we have already referred. There was the least 

 during the middle hours of the night, a slight increase with sunlight, a large 

 increase after the meals, and a decrease before them, and a prolonged and 

 inevitable fall after about 9 o'clock P.M. The proportion in the night of six 

 hours to the clay of 18 hours was in himself as 1 : 1.8. Most persons are 

 conscious of a greater difficulty in bearing exposure to cold between mid- 

 night and early morning, than at any other period in the twenty-four hours. 1 



x. Season. Dr. Edward Smith has investigated the influence of season by 

 determining the amount evolved at rest, in the sitting posture, and before 

 breakfast, daily throughout the year, and has found that the greatest amount 

 occurs in April and May ; that there is a decrease commencing in June, and 

 continuing progressively through June, July, and August to September; 

 and that in October, November, and December there is an increase. He 

 considers that there is a maximum period (end of Winter and Spring"), a 

 minimum period (end of Summer to Autumn), an increasing period (Win- 

 ter), and a decreasing period (early Summer). The extreme loss at the end 

 of Summer was 3 grains of Carbonic acid per minute, or 33 per cent., and 

 on the monthly average the loss was 17 or 18 per cent. He has applied this 

 to the causation and treatment of disease, and has shown that the influence 

 of the rotation of the seasons is a prime element in the vis medicatrix nntitnr. 

 Temperature and Barometric pressure to some extent, but very imperfectly, 

 explained the results. A medium temperature was accompanied by the most 

 diverse quantities of Carbonic acid at the different seasons, but extremes 

 exhibited marked influence. 



XI. Frequency of Respiration. Vierordt 2 found that, if he only respired 

 six times in a minute, the quantity of Carbonic acid was 5.5 per cent, of the 

 whole air exhaled ; with twelve respirations, it was 4.2 ; with twenty-four, it 

 was 3.3; with forty-eight, it was 3.0; and with ninety-six, it was 2.6 per cent. 

 In some of the experiments of Messrs. Allen and Pepys, it was as much as 

 8 per cent. If the breath be held for 40 seconds (Vierordt), or 100 seconds 

 (Stefan ), the proportion of Carbonic acid may rise to upwards of 7^ per cent., 

 and if the same air be breathed over and over again, the proportion may 

 attain 9 per cent. (Miiller, Setschenow). 



xii. State of Health or Disease. Upon this very important cause of vari- 

 ation, few accurate researches have yet been made. The percentage of Car- 



1 Perhaps the smaller quantity of CO 2 exhaled by night than by day is due to less 

 food being taken at this time. See the experiments of Hennehcrg, E. Schulze, 

 Marker, Uusse on Sheep, in Centralblatt f d. Mod Wiss. 1870, p. 3">::. 



' I'hy.-iolngie des Aihmens, pp. 102-149. Panum (Pfliiger's Archiv, Bd. i) and 

 Berg (. \rdiiv f. Klin. Mod., Bd. vi) arrived at the same results as Vierordt, but 

 Jju-M-n ( /e it sch rift f. Biologic) thinks that when the respirations are simply increased 

 in number in a given time their greater shallowness compensates for their increased 

 frequency, and no more CO 2 is given on". 



