COMPOSITION OF EXPIRED AIR. 



255 



3. Respiratory Quotient. Hence, during respiration, more O is 

 taken into the body from the air than C0 2 is given off (Lavoisier) ; so 

 that the volume of the expired air is (T<T- sV) smaller than the volume 

 of the air inspired, both being calculated as dry, at the same tempera- 

 ture, and at the same barometric pressure. The relation of the O 

 absorbed to the C0 3 given off, is 4'38 : 4'782. This is expressed by 

 the " respiratory quotient " 



\ 4-Z82 



4. An excessively small quantity of 1ST is added to the expired air 

 (Regnault and Eeiset). Seegen found that all the N taken in with the 

 food did not reappear in the excreta (urine and faeces), and he assumed 

 that a small part of it was given off by the lungs. 



5. During ordinary respiration, the expired air is saturated with watery 

 vapour. It is evident, therefore, that when the watery vapour in the 

 air varies, the lungs give off different quantities of water from the 

 body. The percentage of watery vapour falls during rapid respiration 

 (Moleschott). 



6. The expired air is WARMER (36'3C), that is, very A 

 near the temperature of the body, and even although 



the temperature of the surrounding atmosphere be very 

 variable, the temperature of the expired air still remains 

 nearly the same. 



The Instrument (Fig. 114) was used by Valentin and Brunner 

 to determine the temperature of the expired air. It consists of a 

 glass tube, A, A, with a mouth-piece, B, and in it is a fine 

 thermometer, C. The operator breathes through the nose and 

 expires slowly through the mouth-piece into^the tube. 



Temperature of the 

 Expired Air. 



.... + 29'8C - 



+ 36-2-37 



Temperature of 

 the Air. 



-6'3C, 

 + 17-19, 



+ 41, 



+ 44, 



+ 38-1 

 + 38-5 



7. The diminution of the volume of the~expired_air 

 mentioned under (3) is far more than compensated by 

 the warming which the inspired air undergoes in the 

 respiratory passages, so that the volume of the expired air 

 is one-ninth greater than the air inspired. 



8. A very small quantity of AMMONIA is found in the 

 expired air (Regnault and Reiset) 0*0204: grammes in 

 24 hours (Lossen) ; it is probably derived from the blood, 

 for blood exposed to the air evolves ammonia (Briicke). 



9. Small quantities of H and CH 4 are expired, both 

 being absorbed from the intestine. In herbivora, Reiset 

 found that 30 litres of CH 4 were expired in 24 hours. 



