CHANGES EFFECTED IN THE AIR. 103 



odour is more pungent ; its temperature is from 98 of 

 Far. raised to 100 ; its capacity for caloric is a lit- 

 tle lessened ; it coagulates more quickly, and is less 

 abundant in serum. 



Emily. Now I may ask how these changes are pro- 

 duced ? 



j} Tf B. And truly a question more easily asked 

 than answered. But at any rate we can tell pretty ex- 

 actly, what changes the air itself has undergone, and if 

 it were true, as was once said by royal lips, that " in 

 a multitude of counsellors there is wisdom," we might 

 be exceedingly wise concerning the changes that are 

 produced in the blood. The air, which we breathe, 

 is composed, you know, of two gases, oxygen and nit- 

 rogen 21 parts of the former, and about 78 of the lat- 

 ter. Besides these, there is generally found a very 

 small portion of carbonic acid about 1 part. Such is 

 the composition of the air when it goes into the lungs, 

 but not such when it comes out. If we examine a quan- 

 tity of expired air, we shall find that the oxygen, instead 

 of forming 21 parts of it, now forms only 18 or 19 parts, 

 that the carbonic acid amounts to 3 or 4 parts, and that 

 the nitrogen is not apparently increased or diminished. 

 So you see that oxygen alone is made use of in the per- 

 formance of this function ; and the rapidity with which 

 its deprivation causes the death of any living being, well 

 entitles it to be considered as the grand supporter of liv- 

 Sng action. 



Emily. Since the nitrogen is returned unchanged in 

 quantity, what can possibly be its use in respiration ? 

 Would not an air of pure oxygen answer the purpose 

 just as well ? 



Dr. B. Though we are unable to see what part the 

 nitrogen takes in the process, numerous experiments 

 prove that it is not useless, nor to be dispensed with ; 

 for though an animal will live four times longer in pure 

 oxygen, than in the same quantity of atmospheric air, 

 yet when breathed for any length of time, the organ 



