692 



SCIENCE 



[Vol. LVI, No. 1459 



respiratory epithelium generally, parts of tlie 

 aildmentary epithelium, 'tihe pleura, and the 

 museles of the tlhoraeie wall, the diaphragm, 

 and the abdominal muscles. 



The afferent pa'tlis lare (1) the vagus (temth 

 cranial nerve) from the lungs and fa-achea, the 

 fifth cranial from ithe mucous membrane of the 

 nose, the glossopharyngeal (ninth cranial) from 

 the pharynx and tlie portions of the soft palate, 

 the phrenic^ from the diaphragm, the sym- 

 pathetii'c'' fi-om the thoracic wall, and the dorsal 

 roots of the spin^al nerves from the thoracic 

 and abdom'inal museles. 



Th« central connections of the vagus do not 

 necessarilj' extend heyond hhe medulla obloaig- 

 ata. The central oonneotion of the spinal 

 tracts airisiing from dorsal root fibers are pri- 

 marily with the mid-brain (regiotn of the cor- 

 pora quadrigemina) and only secondarily witih 

 the medulla oblongata. 



We have no evidence of any -true respira- 

 tory mechanisms of an accessory sort in the 

 spinial cord. The efferent root cells in the 

 spinal cord have no special sensitiveness to car- 

 bon dioxide. 



The respiratory rate becomes slower after 

 division of both vagi for ttlie a-©ason that affer- 

 ent impulses over the vagi, which are normally 

 summed with the carbon dioxide in the 'blood 

 to produce an excitation of the cells of the 

 medulla, are no longer present, and tihe excita- 

 tion of the centi-al cells is mow dependent in 

 large part upon the cai-bon -dioxide alone. The 

 form of the respiratory movements changes 

 for the same reason that the movements of a 

 limh undergo a dhange in character when the 

 afferent nerves from the limb are divided, i.e., 

 both types of movements become ataxic. 



A further fall in the respiratory rate ensues 

 wlien, in addition to. division of the vagi, there 

 is section of the dorsal roots of the spinal 

 nerves or 'transection at 'the lower border of 

 the midbnain because there is a still greater loss 

 of afferent nerve impulses, and excitation of 

 the efferent cells in the medulla oblongata be- 

 comes almost wlioUy dependent upon the cai-- 



3 Mathison, G. C, Review of Neurol, and Psychi- 

 atry, 1912, X, 553. 



4 Barry, D. T., Journ. Physiol., 1912, xlv, 473. 



ibon dioxide of the blood. The respiratory 

 movements 'also 'become correspondingly more 

 ataxic. 



Costal movements of respiration fail after 

 'section of the dorsal roots alone for the reason 

 that the efferent root cells of 'the intercostal 

 nerves, wluch are noiinally excited by impulses 

 from 'at least two sources — the descending res- 

 piratory motor fibers and the dorsal roots of 

 'the initei'costal nei'ves — now receive impulses 

 from the descending fibere only. There is no 

 actual paralysis of the efferent root cells, since 

 eos'tal movements 'are immediately resumed 

 when contraction of the di-aphragm is prevent- 

 ed. This indicates ithat von Monakow's dia- 

 schisis effect is due to loss of some nervous 

 impulses normally enitering into the process of 

 excitation of a motor cell. 



Our idea of the manner of action of the 

 nervous mechanism for respiration may be 

 briefly stated 'as follows. Afferent impulses 

 passing into the central mechanism in 'the 

 medulla oblongata reach 'the efferent cells 

 'through connections wthich do not p'ass out- 

 side of tOie medulla itself. The central path- 

 ways of afferent limpulses over the sympathetic 

 fibers and the p'hrenies 'are at present unknown. 

 Afferent im'pulses coming in over the dorsal 

 roots of ;tlie spinal nei-ves a-eaeh Sae efferent 

 root cells through intra-spinal -connections, but 

 the discharge of these cells is witiiheld until 

 the arrival of impulses over the descending 

 'tra'cts in ithe spinal cord. Impulses from these 

 two sources are summed in the excitation of the 

 efferent root cells. Otther -impulses from the 

 doi'sal root fibers pass up the spinal cord to 

 the region of ithe corpora quadrigemina, but 

 whether over 'the ventral spino^thal'amie fibers^' 

 or over fibers in the spino-cerebellar tracts is 

 uncertain. From the midbrain, these 'impulses 

 are relayed to the cells of the respiratory cen- 

 ter in the medulla oblongata. The excitation 

 of these cells is dependent upon the summation 

 of stimuli arising from (1) the concentration 

 of carbon dioxide in the blood flowing through 

 these cells, and (2) the nervous impulses com- 

 ing in over the various afferent paithways. The 



n Eansom, The Anatomy of the Nervous Sys- 

 tem, Philadelphia, 1920, p. 104. 



