The passage of the faeces along the intestinal canal from the stomach to the anus may be obstructed by various impediments.

1. As has been already stated, constipation is one of the most frequent causes of obstruction. Deficient secretion from the intestinal mucous membrane, and want of peristaltic action in the muscular coat, lead to accumulation of faeces, and then to impaction of the hardened excrement. The lodgement is generally found situated in the rectum, and can be easily made out by digital examination.

2. The dog is peculiarly exposed to obstruction from swallowing non-digestible substances. Blaine mentions a case of obstruction in the jejunum caused by a cork which had been forced down the dog's throat by some wretched brute who ought to have had his own gut tightly corked up. Professor Simond narrates a case, in which, after obstinate constipation, feverishness, loss of appetite, occasional vomiting, and pain and distention of the belly, a common pebble was found in the bowel. It had passed through the stomach and some distance along the intestine, producing intense inflammation, until it had reached a certain point, where it became fast. The dog had been used to fetch such stones out of the water. Mr Goodwin found in the bowels of a dog three balls of hair, of different sizes, the largest being about the size and shape of a hen's egg. These bodies were covered or intermixed with earthy matter. The bowel had accommodated itself to these unusual contents, as the largest ball was found in a kind of sac. As the ball grew the canal widened and thickened.

There was not absolute stoppage of the bowels, for watery evacuations made their way past the lodgements. In another case, the splinter of a chicken-bone was found blocking up the canal, and causing irremovable obstruction. I was recently called in to an old, and almost toothless, dog, belonging to Sir John M'Neill. The dog strained violently without result. I found a hard substance in the rectum, on making a digital examination of that part; it proved to be the cervical vertebrae of a fowl. Pins and needles have also been known to occasion the same results. In short, any body that resists the solvent action of the digestive juices may, if large enough, give rise to mechanical obstruction.

The recital of these different causes of a disorder which always exposes the dog to intense suffering, and which often destroys life, will be sufficient to show how strict one should be in preventing the use of bones, especially chicken bones, as an ordinary article of diet. The trick of teaching dogs to run after sticks and stones, not only inflicts certain damage on the teeth, and consequently renders mastication of food imperfect, but also exposes them to the risk of swallowing these bodies. And although recovery may take place, after the discharge of even comparatively large bodies, yet the animal's life is placed in extreme danger.

Any foreign body that has been swallowed must be ejected as soon as possible before it has got out of the stomach, by the mechanical act of vomiting. This will have to be induced by an emetic* A considerable supply of thick gruel should be forced down to afford, bulk upon which the stomach, aided by the diaphragm and abdominal muscles, can efficiently contract. Should these means, even though promptly resorted to, fail in producing the desired effect, the symptoms of irritation, spasm, and inflammation, that are almost sure to mask the passage of the substance along the bowel, must be treated according to the circumstances of the case.†

3. Another occasional cause of obstruction is intussusception - a condition in which part of the bowel narrowed by spasm slips into another part, having the natural diameter, and becomes invagin-ated therein. The consequence is that the faeces are unable to pass by the mechanical impediment thus formed; they accumulate, and colic and enteritis follow. During life it is anything but easy to distinguish with certainty intussusception from enteritis; or to deduce from the symptoms trustworthy data as to the real nature of the existing lesion. This untoward accident is usually preceded by colic, and it is to the irregular action of the muscular coat that the invagination is then attributable. The symptoms of enteritis shortly come on. Indications of severe and persistent pain, tenderness of the belly, vomiting and reversed peristaltic action, insuperable obstruction, and the rejection of enemata, usually point out intussusception.

* See page 72.

† See "Colic" and "Enteritis".

4. Obstruction is a symptom of peritonitis and enteritis, the inflammation acting as the primary cause. It may also follow peritonitis or enteritis as a secondary effect of the inflammatory action, the contractility of the muscular coat being diminished thereby. The dog's rectum is peculiarly liable to become inflamed. But although obstruction may "be both the secondary result of inflammation, yet it may also be in other cases the direct cause of inflammation, as has been already pointed out.

5. Obstruction in dogs has been occasionally known to result from twists or displacement of the intestine, which have been produced by violent exertion; or by the irregular action and spasm of the bowel present in colic; or by the strong contraction of a coil of intestine against impacted faeces, tending to cause rolling over of the bowel. There are of course symptoms of obstruction, followed by those of enteritis, and ending in death from gangrene.

6. Obstruction is occasionally met with in the result of strangulated hernia.