586 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



additional effort is termed the reserve volume, and also amounts to about 

 one hundred and ten cubic inches. After a forced expiration there is 

 still a certain amount of air which cannot possibly be forced out of the 

 lungs ; this constitutes what is termed the residual volume, and also 

 equals about one hundred and ten cubic inches. 



The vital capacity volume is the amount of air which man is 

 capable of expiring by the greatest expiratory effort after the greatest 

 inspiratory effort. It includes the complemental volume, the breathing 

 volume, and the reserve volume, and is, therefore, the amount of air 

 which may be displaced in respiration. It has been shown by Dr. 

 Hutchinson that this volume bears a relation to the height of the 

 individual, which is especially remarkable when we recollect that the 

 height of individuals depends upon the length of the legs, and not upon 

 the trunk, the same persons who may vary greatly in height while 

 standing exhibiting but slight difference in height when sitting. It is 

 curious, also, to observe that the vital capacity does not depend upon 

 the capacity of the chest so much as upon the degree of mobility. Thus, 

 a man of greater girth may have less amount of vital capacity than 

 another with less girth but greater mobility of the walls of the chest. 

 Mr. Hutchinson has constructed an instrument for measuring this vital 

 capacity volume. It consists of a bell-jar so mounted as to be readily 

 displaced by the power which is exerted by the air in passing from the 

 mouth and air-passages. With the interior of the bell-jar communicates 

 a tube and attached mouth-piece. The person to be experimented upon 

 takes a deep inspiration, and then breathes out by the tube by a forced 

 expiration, which causes the bell-jar to rise, and the number of cubic 

 inches thrown out is measured by a graduated scale, suitably placed to 

 indicate the rise and fall of the bell-jar. As a result of these experi- 

 ments it was found that every inch added to the height of an individual 

 increases about eight cubic inches the vital capacity. This appears upon 

 examination of the following table : 



The age has a marked effect upon the vital capacity volume ; the 

 volume increases from 15 to 30, remains about stationary from 40 to 45, 



