456 THE RESPIRATORY MECHANISM. 



cord be heightened by small doses of strychnine, even spon- 

 taneous efforts of breathing may occasionally be observed." 

 . . . "Since in such cases the rhythmically repeated move- 

 ments of the respiratory muscles are sometimes accompanied 

 by rhythmic movements of the fore- and hind- limbs not re- 

 spiratory in nature, it may be doubted whether these experi- 

 ments really prove the existence of distinct respiratory centers 

 in the spinal cord/' That the data previously given further 

 tend to diminish the likelihood that any such center exists 

 seems obvious. 



And still the existence of such a center seems to be sus- 

 tained by experimental evidence. Thus, division of the cord 

 below the seventh cervical nerve arrests costal respiration; 

 section below the medulla causes all thoracic movements to 

 cease; removal of the brain above the medulla, the seat of the 

 supposed center, does not stop respiration, while cessation of 

 this function occurs when the medulla is removed or exten- 

 sively injured, save in exceptional cases. After reviewing this 

 evidence Professor Foster adds: "Nay, more; if only a small 

 portion of the medulla a tract whose limits have not been 

 clearly defined, 20 but which may be described as lying below 

 the vasomotor center in the immediate neighborhood of the 

 nuclei of the vagus nerves be removed or injured, respiration 

 ceases, and death at once ensues. Hence this portion of the 

 nervous system was called by Flourens the vital knot, or gan- 

 glion of life: noeud vital We shall speak of it as the respira- 

 tory center." 



The first question that suggests itself is the following: Can 

 the respiratory center be a portion of the vagus center, in the 

 immediate neighborhood of which it is generally located? 

 Professor Foster remarks, in this connection: "In attempting 

 to decide this question we naturally turn to the pneumogastric 

 as being the nerve most likely to serve as the channel of 

 afferent impulses setting in action the respiratory center. If 

 both vagus nerves be divided, respiration still continues, though 

 in a modified form. 21 This proves distinctly that afferent im- 

 pulses ascending those nerves are not the efficient cause of the 



10 The italics are our own. 

 21 All italics are our own. 



