CHAPTER VI. 



THE ADRENAL SYSTEM AND VASOMOTOR 

 FUNCTIONS. 



THE OXIDIZING SUBSTANCE AND THE MOTOR NERVES IN 

 THEIR RELATION TO MUSCULAR CONTRACTION. 



DIVISION of the spinal cord below the medulla oblongata 

 is followed by dilation of all the vessels of the organism, while 

 electrical stimulation of the lower cut segment of the cord 

 causes constriction of these blood-vessels and a general rise 

 of blood-pressure. Evidently constriction and dilation of the 

 vessels of the organism are regulated by centers located in the 

 medulla and pons, in accordance with the present teachings. 

 We are, therefore, referred to these centers for the impulse- 

 waves (transmitted through the vasomotor nerves) which gov- 

 ern the structures that co-operate with the adrenal system in 

 the performance of its physiological functions. What is the 

 nature of the relationship between the adrenal system and the 

 vasomotor system? 



A cursory analysis of this question soon reveals an impor- 

 tant feature, namely: that the voluntary, or skeletal, muscular 

 system cannot be classed with the other organs in respect to 

 vasomotor functions. The sympathetic system is the essential, 

 perhaps the only, source of vasoconstrictor nerves, and yet this 

 system is not known to extend to the extremities. Again, 

 vasoconstrictors and vasodilators are said to accompany the 

 larger nerve-bundles, the sciatic, for instance; but a survey 

 of the field distinctly shows that the evidence as to the ex- 

 istence of separate vasoconstrictors is purely inferential. Since 

 the sympathetic nerve does not appear to send subdivisions to 

 this class of muscles, the association of constrictors of another 

 source introduces an element of confusion, not only as regards 

 the peripheral structures themselves, but particularly in re- 

 spect to the central origin of the two systems classed under 

 the one single term of "vasomotors." As it is impossible to 



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