544 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



diminishes the relative percentage of O absorbed increases, and this continues 

 until the volume in the inspired air is reduced to 11.26 per cent., 27 per cent, 

 of which is absorbed; below this point no further increase of absorption 

 occurs. As the quantity of O absorbed is reduced the respiratory quotient 

 becomes greaier, and may reach as high as 2.218. 



When the quantity of O remains at the normal standard and the percentage 

 of CO 2 is much increased, the elimination of the latter is interfered with ; and 

 Pfliiger has shown that if the percentage of CO 2 be high, dyspnoea ensues, 

 notwithstanding the fact that the blood contains a normal amount of O. 

 When air contains 3 to 4 volumes per cent, of CO 2 , the quantity of CO 2 

 given off is diminished about one-half. Speck l and others have found that 

 the elimination of CO 2 during a given period may be independent of both 

 the percentage of O in the inspired air and the quantity absorbed. An atmo- 

 sphere containing 10 volumes per cent, of CO 2 is generally believed to be toxic, 

 but Wilson's 2 investigations show that air having even as much as 25 to 30 

 volumes per cent, may be inhaled with impunity. It is quite probable that 

 in those cases in which small percentages of CO 2 in the inspired air have 

 proven poisonous the gases were contaminated with CO (carbon monoxide). 

 Respiration of an atmosphere of pure CO 2 is followed within two or three 

 minutes by death. 



Worm-Muller found that when animals breathe atmospheric air in a large 

 closed chamber O disappears and CO 2 accumulates, and death finally occurs, 

 not from a lack of O, but from the increase of CO 2 , as is shown by the fact 

 that at the time of death the quantity of O in the air is sufficient to sustain 

 life. He has also shown that animals placed in an atmosphere of pure O die 

 from an accumulation of CO 2 in the blood, rabbits succumbing after the reten- 

 tion of a volume of CO 2 equal to one-half the volume of the body, and at a 

 time when the atmosphere contained as much as 50 volumes per cent, of O. 



The dyspnoea occurring in an animal confined in an air-tight chamber of 

 small size is due to the lack of O, nearly all of the gas being absorbed before 

 the animal dies. If a cold-blooded animal, such as a frog, be similarly ex- 

 posed, the attraction of haemoglobin for O is so strong that almost every par- 

 ticle of gas will pass into the blood long before death occurs ; and even after 

 the total disappearance of O the elimination of CO 2 is said to continue at the 

 normal rate. 



Animals placed in a confined space become accustomed, as it were, to the 

 vitiated air, and survive longer than a fresh animal suddenly thrust into the 

 poisonous atmosphere. 



The Respiratory Quotient. The relation between the quantities of O 

 absorbed and CO 2 given off during a given period is expressed as the respira- 

 tory quotient. The air during its sojourn in the lungs loses 4.78 volumes per 

 cent, of O and acquires 4.34 volumes per cent, of CO 2 , hence the respiratory 



CO 4 34 

 quotient is ^~ '~ = 0.901. This quotient is subject to considerable 



V^/ TX* I O 



1 Loc. cit. * American Journ. Pharmacy, 1893, p. 561. 



