BLOOD. 127 



periods of the day. He found that during equal spaces of 

 time the minimum occurred during the middle of the night ; 

 towards morning it increased, and attained its maximum be- 

 tween 1 1 and 1 o'clock ; it then gradually diminished till 

 about 9 p. m.., when it remained fixed at its minimum till 

 3 a. m. The quantity of carbonic acid was likewise found to 

 increase by gentle exercise, especially at its commencement, 

 and when the barometer was low. 



The mean amount of carbonic acid per cent, was 3-45. 

 [A series of similar experiments has been published by Mr. 

 Coathupe, which differ in several respects in their results from 

 those of Prout. They were continued for a week. The fol- 

 lowing is the result obtained : 



Carbonic acid per cent, 

 of air expired. 

 From 8 a.m. to 9| . . . . 4-37 



3-90 



3-92 



417 



3-63 



10 a.m. to 12 

 12 noon to 1 



2 p.m. to 5^ 



7 p.m. to 8^ 



9 p.m. to midnight 



4-12— Mean 4-02. 



Macgregor ascertained that the air expired by persons ill of 

 confluent smallpox contained as much as 8^ of carbonic acid. 

 During the eruptive fever of measles, it amounted to from 4 to 

 5g ; and in proportion as the health was restored, the per cent- 

 age was diminished to its natural standard. In chronic skin 

 diseases an augmentation was likewise observed ; and, in a case 

 of ichthyosis, the mean per centage was 7*2 ; in tjqihus, ac- 

 cording to Dr. Malcolm,' the formation of carbonic acid is di- 

 minished; in diabetes, no deviation from the normal standard 

 could be detected. 



The question of the quantity of carbonic acid expired by a 

 person in twenty-four hours has lately become of peculiar inte- 

 rest, in consequence of its association with several problems of 

 high physiological importance. Liebig has endeavoured indi- 

 rectly to estimate the quantity by comparing the amount of 

 carbon contained in the food consumed in the twenty-four 

 hours, with the carbon of the excretions during the same period, 

 and estimating the difference as the quantity separated by the 

 respiratory process. He thus found that an adult, taking 

 moderate exercise, expires daily on an average 13-9 ounces of 

 carbon (more than double the quantity found by Lavoisier.) 



' London and Edinburgh Monthly Journal of Medical Science, 1843, page 1. 



