RESPIRATION IN THE CHELONIA. 37 



of a month and then exhibited no marked evidence of diseased lungs. In others, 

 there was occasionally found an abscess at the base of the neck. This pathological 

 occurrence is, however, a common one in turtles caught with the hook, and cannot, 

 with any probability, be supposed to he due to the section of the pneumogastric. 



The only striking effect of this section was, the constant sensibility which the 

 nerve then exhibited. At the moment of dividing or crushing it, the animal showed 

 every possible evidence of acute pain. Irritation of the centric end of the cut nerve 

 gave rise to like phenomena, while stimulation of the peripheral end caused no such 

 results. 



A number of careful experiments were made to ascertain whether these irrita- 

 tions of the nerve produced any instant effect, either upon the inspiratory or 

 expiratory muscles of the breast-box. But in no case did the stimulation seem to 

 influence them to movement. 



( ialvanization of the pneuinogastric nerve in turtles arrests the heart's move- 

 ments. Gentle irritation of the trunk causes the heart to beat more rapidly. Sec- 

 tion of one nerve causes the heart to quicken its pulsations. Division of both nerves 

 induces still more rapid action, but in either ease the heart, after a few hours, 

 regains its original rate of pulsation. 



The nerves which supply motor endowments to the internal respiratory muscles 

 need no special illustration here. They are fully described in the anatomical sec- 

 tion of this essay. It only remains to add, that their office and relation to the 

 muscles was tested by stimulating them with galvanism and by dividing them, so 

 as to cause paralysis of the muscles in question. 



The centre, to which proceed impressions, giving rise therein to respiratory 

 impulses, appears to be, as in other animals, the medulla oblongata. The site of 

 the respiratory ganglions would scarcely have attracted our attention, however, had 

 it not been, that, in the following experiment, a fact was noticed which induced us 

 to examine the question more fully. 



Experiment. — In a turtle previously used to examine the offices of the laryngeal 

 nerves, and in whom the glottis could still open on one side, we divided the cer- 

 vical spine at its upper third, and continued to watch the respiratory muscles. To 

 our surprise the flank muscles acted at intervals for thirty minutes, but the 

 two sides no longer moved synchronously. At one moment the right muscle 

 contracted, at another the left, and the movements of both were irregular and some- 

 times incomplete. 



It appeared to us, that these motions after section of the spine might be merely 

 the rhythmic repetition of habitual movements, such as, according to Brown- 

 Sequard, appear sometimes in the diaphragms of mammals even. Long after these 

 muscles in the turtle ceased to move, all the other reflex acts continued, and 

 excepting these, almost every muscle below the point of section could be excited 

 easily to reflex motion ; neither was there any longer a synchronism of action 

 between the respiratory muscles of the glottis and those of the breast-box. 



Experirru nt. — Turtle, weight six pounds. In this case, also, the cervical spine was 

 divided, but although the reflex activity of most of the parts below the section was 

 remarkable, the respiratory muscles alone failed to respond to excitation of distant 



