144 EESPIEATIOK 



consumed per hour. The estimate arrived at by Longet, from a comparison of the re- 

 sults obtained by different reliable observers, is perhaps as near the truth as possible. 

 This estimate puts the hourly consumption at from 1,220 to 1,525 cubic inches, "in an 

 adult male, during repose and in normal conditions of health and temperature." 



In passing through the lungs, the air, beside losing a proportion of its oxygen, 

 undergoes the following changes : 



1. Increase in temperature. 



2. Gain of carbonic acid. 



3. Gain of watery vapor. 



4. Gain of ammonia. 



5. Gain of a small quantity of organic matter. 



6. Gain, and occasionally loss, of nitrogen. 



The elevation in temperature of the air which has passed through the lungs has been 

 carefully observed by Dr. Grehant. He found that, with an external temperature of 72 

 Fahr., respiring seventeen times per minute, the air taken in by the nares and expired by 

 the mouth, through an apparatus containing a thermometer carefully protected from ex- 

 ternal influences, marked a temperature of 95*4. Taking in the air by the mouth, the 

 temperature of the expired air was 93. At the commencement of the expiration, Dr. 

 Grehant noted a temperature of 94. After a prolonged expiration, the temperature 

 was 96. In these observations, the temperature taken beneath the tongue was 98. 



Exhalation of Carbonic Acid. The production of carbonic acid in the respiratory 

 process is as universal as the consumption of oxygen. Experiments have shown that all 

 animals during life exhale this principle, as well as all tissues, so long as they retain their 

 irritability. This takes place, not only when the animals or tissues are placed in an 

 atmosphere of oxygen or common air, but, as was observed by Spallanzani, in an 

 atmosphere of pure nitrogen or hydrogen. This fact has since been noted by W. F. 

 Edwards, J. Muller, G. Liebig, Bert, and others. 



The study of the exhalation of carbonic acid presents several problems of great 

 physiological interest : 



1. What is the absolute quantity of carbonic acid exhaled by the lungs in a given 

 time? 



2. What are the variations in the exhalation of this principle due to physiological 

 influences ? 



3. What is the relation between the quantity of carbonic acid produced and the 

 quantity of oxygen consumed ? 



On account of the variations in the quantities of carbonic acid exhaled at different 

 periods of the day, and particularly the great influence of the rapidity of the respiratory 

 movements, it is exceedingly difficult to fix upon any number that will represent the 

 average proportion of this gas contained in the expired air. The same influences were 

 found affecting the consumption of oxygen, and the same difficulties were experienced 

 in forming an estimate of the proportion of this gas consumed. As we assumed, after 

 a comparison of the results obtained by different observers, that the volume of oxygen 

 consumed is about five per cent, of the entire volume of air, it may be stated, as an 

 approximation, that, in the intervals of digestion, in repose, and under normal conditions 

 as regards the frequency of the pulse and respiration, the volume of carbonic acid 

 exhaled is about four per cent, of the volume of the expired air. As the volume of 

 oxygen which enters into the composition of a definite quantity of carbonic acid is pre- 

 cisely equal to the volume of the carbonic acid, it is seen that a certain quantity of 

 oxygen disappears in respiration and is not represented in the carbonic acid exhaled. 



There are great differences in the proportion of carbonic acid in the expired air, 

 depending upon the time during which the air has remained in the lungs. This interest- 



