366 EXAMPLES OF CHEMICAL CORRELATION 



Stimulation of this area enhances the rate and amplitude of the res- 

 piratory movements. Its narcotization or injury depresses or annuls 

 the respiratory movements. The actual synchrony is therefore not 

 directly between the skeletal muscles and the respiratory muscles, 

 but between the skeletal muscles and the nervous tissues of the 

 respiratory center. Here we have an even less obvious relationship 

 between tissues which nevertheless act in perfection of harmony, and 

 the source of this harmony lies in a chemical and not in a spatial or 

 mechanical interdependence of the tissues which participate in it. 



The initial effect of deprivation of oxygen or of interference by 

 mechanical or other means with the entrance of air into the lungs is 

 an increased amplitude and frequency of the respiratory movements, 

 a condition which is designated Hyperpnea. This is succeeded by the 

 stage of Dyspnea, in which the still more rapid movements become 

 almost convulsive in character, until finally every muscle which can 

 directly or indirectly assist in the effort to fill or empty the lungs is 

 brought into i itense activity. This activity is quite uncontrollable, 

 as the reader may convince himself by the simple endeavor to "hold 

 the breath" for a prolonged period. If, finally, the lack of oxygen, or 

 obstruction to the passage of air, still defeats the object of these 

 exertions, a relatively sudden cessation of respiratory convulsions sets 

 in, due to paralysis of the respiratory center, and the animal or man is 

 now said to have suffered Asphyxia. If, on the contrary, instead of 

 deprivation of oxygen or obstruction to the intake or exit of air, we 

 have an exceptionally efficient ventilation of the lung, by forcible and 

 repeated inflation or by a series of rapid and very deep voluntary 

 breathing movements, then a condition of temporary suspension of 

 the activity of the respiratory center sets in, a condition known as 

 Apnea, which is purposely cultivated by divers and swimmers before 

 undertaking a period of prolonged immersion below the surface of 

 water. Either no desire to breathe is experienced for a perceptible 

 interval, or the desire is very easily controlled by a voluntary effort. 



After a somewhat longer lapse of time than usual, however, the desire 

 to breathe is again acutely felt, and the respiratory movements there- 

 after become again uncontrollable by any effort of the will. 



Now the effects of suspended breathing are twofold. In the first 

 place the supply of oxygen to the blood, and therefore to the tissues, is 

 cut off and the available oxygen in the body, free or combined in 

 easily dissociable compounds like Oxyhemoglobin is soon exhausted by 

 the irreducible minimum of oxidative change which accompanies the 

 life of all the tissues. In the second place the carbon dioxide which 

 ultimately results from these oxidations cannot escape from the body, 

 and therefore accumulates in the blood and in the tissues. 



The stimulated activity of the respiratory center which accompanies 

 inadequacy of respiration is due to some change in the blood which 

 irrigates it. This is conclusively shown by the fact that if the cerebral 

 circulations of two animals be "crossed," so that the blood from the 



