CHAPTER XVI. 

 EXAMPLES OF CHEMICAL CORRELATION. 



THE CHEMICAL CORRELATION OF RESPIRATORY ACTIVITIES. 



The normal Respiratory Movements of the diaphragm and inter- 

 costal muscles are adjusted to the average need for oxygen which is 

 imposed by the normal functional activities of our tissues. The per- 

 formance of function and the maintenance of the temperature of the 

 body necessitate an expenditure of energy which, since the Hydrolyses 

 which occur in living tissues are usually but slightly exothermic, must 

 be derived for the greater part from energy liberated by Oxidations. 

 As the tissues which are primarily concerned in the performance of 

 mechanical work are the muscular tissues, variations of their activity 

 may most clearly be seen to necessitate corresponding variations in the 

 rapidity and extent of the oxidations upon which their power of per- 

 forming work depends. Of all the various tissues of the body, in fact, 

 the muscles are subject to the most sudden and extreme variations of 

 functional activity, being at the one moment in the state of moderate 

 tension which is the normal condition of rest, and at the next expending 

 all the energy required, for example, to lift the whole weight of the 

 body up a steep incline. To provide a sufficient oxygen supply to 

 render possible at all times, without alterations of the respiratory 

 rhythm, the maximal expenditure of energy by the skeletal muscles, 

 would require a very great wastage of energy by the respiratory muscles 

 themselves, or else the relegation of an excessive proportion of the 

 bodily volume to performance of respiratory functions. The mechan- 

 ism actually and normally employed provides an amplitude of oxygen 

 for customary and moderate needs and when the oxygen requirements 

 of the skeletal muscles renders the customary means of ventilating 

 the body insufficient, then the efficiency of ventilation is temporarily 

 enhanced by a very decided increase in the frequency and amplitude 

 of the respiratory movements. 



Now there is no immediate or obvious connection between the move- 

 ments of the respiratory muscles and those of the skeletal muscles. 

 There is no anatomical or mechanical connection or association be- 

 tween them that would render it a priori probable that the motions of 

 the one group of muscles would tend to synchronize in frequency and 

 extent with those of the other. Moreover, the respiratory movements 

 in the adult higher vertebrates are known to be primarily under the 

 control of a particular region of the Medulla Oblongata, situated in 

 floor of the fourth ventricle, and designated the Respiratory Center. 



