IV. NERVOUS FUNCTIONS. 



GENERAL CONSIDERATIONS. 



THERE is a most intimate relationship existing between the 

 different organs of the body so intimate, indeed, that not one of 

 the whole number can be 'said to be entirely independent of the 

 others. Many illustrations of this dependency might be given, but 

 one will suffice. 



The respirations of an individual at rest are not far from 16 

 per minute, and the pulsations of the radial artery are, under the 

 same condition, about 70. If, now, he exercises violently, the 

 respirations will be found to have greatly increased, amounting 

 perhaps to 30 per minute, while at the same time the pulsations 

 of the artery will have reached 120 per minute. Is this change 

 from the quiescent condition a mere coincidence, or is there a 

 reason for it? If the latter, how has the change been brought 

 about? 



During a resting condition the muscles of the body do not 

 make great demand upon the blood, and with the heart beating 

 70 times per minute the muscles, as well as the other tissues, are 

 receiving all the material they need for the performance of their 

 functions. The 16 respirations a minute are also sufficient to 

 supply the blood with all the oxygen required and to remove from 

 it the necessary amount of carbon dioxid. When, however, the 

 muscles are called upon for the increased exertion above referred 

 to, they must have a greater supply of the necessary materials, to 

 furnish which a larger amount of blood must be sent to them. 

 Then, too, as a result of the extra work, more muscular tissue is 

 wasted, and the waste must be taken away rapidly to the organs 

 whose duty it is to eliminate it. To send the larger supply of 

 blood the heart must beat faster, and to provide the increased 

 oxygen and to remove the additional carbon dioxid the respiratory 

 movements must be more rapid. The muscles of the body have 

 not the power within themselves to increase their activity, but 

 when acted upon properly from without they have. Neither has 

 the heart-muscle the power to beat more quickly until influenced 

 thereto by some influence outside itself. Equally powerless are 

 the agencies which produce the respiratory movements. These 

 outside influences, by which the muscles contract and by which 

 the heart and the respiratory apparatus act in harmony, are 



460 



