138 



OF FOOD, AND THE DIGESTIVE PROCESS. 



FIH. 59. 



m 



the state of distension of the tube ; the fulness or emptiness of the blood- 

 vessels ; the venous or arterial condition of the blood circulating through 

 the tissues, and the temperature at which the experiments are conducted. 



The inquiry is further complicated by 

 the fact that the splanchnic nerves, 

 which are the vaso-motor nerves of the 

 vessels supplying the abdominal viscera, 

 appear also, under certain circum- 

 stances, to exert an inhibitory influence 

 on the intestinal movements. It may 

 be certainly stated that in the collapsed 

 state, the intestines are quiescent, or at 

 most their movements are extremely 

 slow and feeble ; but as soon as food is 

 propelled into them from the stomach, 

 peristaltic contractions commence, which 

 force the contents onwards. These 

 movements are of a reflex nature, the 

 circuit consisting of centripetal sensory 

 nerve-fibres distributed to the mucous 

 membrane, which convey the impression 

 produced by the presence of food to the 

 ganglia of the plexuses of Auerbach and 

 Meissner, from w f hence an impulse is re- 

 flected to the muscular tissues of the in- 

 testine. The accompanying engraving 

 (Fig. 59) may aid in rendering the in- 



Nervous supply of the Intestines. a, is the 

 posterior column of the spiual cord ; 6, the gray 

 substance with its chain of ganglion cells ; c, 



anterior column: d, great sympathetic; e, ner- fl uence O f the Uei'VOUS System Oil the ill- 

 vous ganglion of mesentery ; f ganglion ofuerve ,. , n- .1 , /-* . ., -, . , 



plexus in the walls of the intestine-^, sphincter testines intelligible. CoiUCldently With 



ani; A, sensory filament running centripetally the entrance of food into the intestines, 



to the ano-spiual centre by the posterior col- the bloodvessels become turgid with 



S^rr^^^^SS^ Wood, f condition that appears greatly 



ter; m, encephalic fibre, conducting the man- to heighten the irritability Ol the lierVO- 



dates of the will to this centre; A-, curves of muscular apparatus, for Stimuli which 



successively wider and wider area showing the provoke 110 response when the vessels 

 implication under stronger and stronger stim- ,. > ., , 



uli, of a progressively increasing number of are Comparatively empty, Will produce 



ganglia, till the cord is at length reached, when Well-marked effects when they are fill!. 1 



pain and various reflex effects on distant parts A large amount of evidence has been ac- 



may be experienced. cumulated, showing that the peristaltic 



movements may be influenced by dis- 

 tant cerebro-spinal and sympathetic centres, but the precise channels through 

 which their influence is transmitted are still undetermined. Schifl"- and 

 Budge, 3 in experiments on cats, observed movements of the intestines follow 

 irritation of the corpora striata, pons Varolii, medulla oblon</<tt<(, and other 

 parts of the encephalon; and the remarkable influence of certain emotions, as 

 fear, in increasing peristalsis, as well as the history of many pathological 

 cases, supports the view that the cerebro-spinal nervous system can act more 

 or less directly upon the intestines. Good evidence that tho fibres by which 

 irritation of the more remote sympathetic ganglia act upon the intestines are 

 contained in the spinal cord, is afforded by the following experiment of M. C. 

 Bernard. The spinal cord is divided below the medulla oblongata, to abolish 

 the influence of the Will. The chest is then opened, and the inferior cervical 



1 Van Bnuim llouckgeest, Pfl liar's Archiv, 1872, p. 298. 



2 Lehrbucli dor Physiologic, 1859. 3 Ib., 



18(32, p. 785. 



