DIGESTION 209 



the other, and where this mechanism fails disease at once 

 arises. 



Probably most liquids rapidly pass out of the stomach, 

 especially so in the horse ; the bulky requirements of this 

 animal could not be contained in the stomach, and in fact if, 

 while an animal is drinking, auscultation be practised, water 

 may be heard passing along the duodenum below the right 

 kidney. 



Little of what has hitherto been said applies to ruminants. 

 The movements of their stomach wall are complex ; the immense 

 muscular pillars of the rumen are capable, as we have seen, of 

 mixing, churning, and revolving the contents of the organ. That 

 rotation occurs is certain from the formation of hair balls from 

 material swallowed by the animal in licking its body, or, in the 

 case of sheep, from wool torn out when scratching themselves, 

 and subsequently swallowed. The rumen and omasum are 

 constantly at work, the rumen contracting a little oftener than 

 three times a minute ; the reticulum, on the other hand, has 

 periods of rest, likewise the true stomach. In the latter the 

 movements must be of a most simple character, such as occurs 

 in the single stomach of other animals. 



The movements of the stomach are excited by the presence of 

 food, or any irritation applied to the mucous membrane. These 

 movements are rendered more energetic by stimulation of the 

 vagus, but even when all the nerves going to the part are divided, 

 the stomach can still contract, which is probably due to the 

 ganglia contained in its walls. The stomach is, in fact, an auto- 

 matic organ. It is supplied by both pneumogastrics, the nerves 

 being non-medullated ; in addition, it obtains sympathetic fibres 

 from the solar plexus, to which the right vagus also sends some 

 fibres (see Fig. 80, p. 228) . In the wall of the stomach ganglia are 

 found with which both the vagus and sympathetic communicate. 

 The vagus may be regarded as the motor nerve of the stomach, 

 while the sympathetic is mainly inhibitory ; stimulation of the 

 vagus leads to contraction of the stomach walls, stimulation of 

 the sympathetic causes dilatation of a contracted stomach and 

 relaxation of the pylorus. The vagus supplies the bloodvessels 

 with dilator fibres, whilst the sympathetic supplies them with 

 constrictor fibres. Section of the vagus in the horse causes 

 paralysis of the stomach, and in other animals, if the movements 

 are not abolished, they are certainly diminished. The result of 

 stomach paralysis is that nothing passes on to the intestines, so 

 that in the horse even large poisonous doses of strychnine may 

 thus fail to cause death by lying inert in the stomach. This 

 experiment demonstrates the uselessness of giving medicine by 

 the mouth in many cases of digestive troubles in the horse ; the 



M 



