The contractions of the empty stomach in dogs were recorded by means of a bromoform manometer connected with a delicate rubber balloon in the stomach. In the dogs the balloon was introduced into the stomach either through a gastric fistula or through the esophagus. We were surprised to note the ease with which a small rubber balloon and rubber-tube attachment can be passed through the esophagus into the stomach in dogs. If gentle dogs are selected for the work and the dogs are handled gently, they make little or no resistance after the first two or three experiments. We have never observed vomiting or gagging in dogs as a result of the introduction or the presence of the stomach tube in the esophagus. On the contrary, the dog with the rubber tube and balloon in the stomach and esophagus will lie quietly for hours in the lap of an attendant, while the tonus and movements of the empty stomach are being registered on the kymograph. Frequently the dog will go to sleep during the experiments. This is especially the case if the dog is covered up with a coat or a comforter. The tube in the esophagus does not cause distress or inhibition of the stomach movements. After some training the dogs do not even chew or bite on the rubber tube in the mouth.
Some of the observations were made on dogs with a fistula in the fundus of the stomach. In our first dog we made use of the classical silver cannula. In all the other dogs we discarded the metal cannula and adopted the surgical methods followed in human gastric fistula cases. The incision (3 to 4 cm. in length) is made 3 cm. below the last rib and 5 to 6 cm. to the left of the linea alba. The oblique and transverse muscles are carefully separated without cutting them. The desired region of the gastric fundus is pulled out through this opening. The peritoneum is sutured to the fundus pouch. The abdominal muscles are similarly sutured to the pouch. In making these sutures care is taken no): to penetrate deeper than the muscle layers of the pouch. The apex of the fundus pouch is then slit open, and the edges sutured to the edges of the skin. A closed rubber tube 1 cm. in diameter is passed through the opening into the stomach and kept in place for 4 days.
Then the tube and dressing are removed. It is found that the abdominal muscles compress this narrow pouch to such an extent that there is virtually no leakage from the stomach, much less leakage, in fact, than even in the most successful fistula using the metal cannula. There is no trouble in closing up of the fistula as long as the animal is being used two or three times a week. The dog takes care of the slight leakage, so there is no corrosion of the skin. We have dogs now in the laboratory with such fistula of 18 months' standing, and the dogs are in the best of condition. In fact, it is obvious that this fistula leaves the stomach much more normal than does the silver cannula method. We have obtained normal hunger contractions of the empty stomach 36 to 48 hours after making the fistula. Nothing like normal hunger contractions is seen in the stomach for 6 to 10 days after making the fistula by means of the metal tube. The old silver tube method should be abandoned in all experimental work on the stomach.
In the beginning of this work the animals were kept suspended in comfortable hammocks during the observations on the gastric hunger movements. It soon became apparent, however, that any kind of mechanical restraint on a young, vigorous, and very hungry dog causes restlessness and evident distress, especially when continued for hours. Training will overcome this in part, but not completely. Distress and restlessness will obviously interfere with the stomach movements. We, therefore, tried the expedient of having an attendant keep the dog snugly in his lap during the observation period. This proved very satisfactory, except for the attendant. It is irksome, to say the least, to sit still for 2 to 8 hours at a stretch. We can appreciate the reason for the dog's restlessness when restrained mechanically in a hammock or on a couch for that length of time. When the attendant knows how to handle dogs, even a very hungry dog will lie in his lap quietly for hours, and will usually cuddle up and go to sleep. After a few experiments most dogs seek the research room by preference, and jump into the attendant's lap voluntarily. Some of our dogs became so well trained that they would lie quietly on a pillow for 2 to 3 hours at a time without any restraint whatever. It is obvious that mental stress and restlessness interfere with the stomach contractions, not only in the way of direct inhibition, but also by the varying tonus and irregular contractions of the abdominal muscles. The animals used in these experiments were mostly young and vigorous females.
The contractions of the empty stomach, as registered by means of a delicate balloon in the fundus, fall into three types according to the degree of tonus of the stomach.
When the stomach shows feeble tonus, the hunger contractions show an average duration of about 30 seconds, and the intervals between the contractions vary from J to 3 or 4 minutes. This type of contractions usually falls into groups, separated by intervals of relative quiescence. The duration of the groups varies from \ to 3 hours, and the number of contractions in each group varies correspondingly. It is very rare that a contraction group of type I ends in a tetanus so frequently observed in man. The group usually begins with feeble contractions but of longer than average duration and relatively far apart, and the contractions become gradually stronger and the intervals shorter. The end of the group is usually characterized by contractions of gradually decreasing strength.
When the stomach is in relatively strong tonus the hunger contractions follow one another in rapid succession, that is, without any intervening pause. The duration of the contractions varies between 20 and 30 seconds. These contractions are frequently interrupted by periods of incomplete tetanus lasting from 1 to s minutes. These periods of tetanus are practially identical with those previously described in man. The contractions of this type do not fall into distinct groups. They may vary to some extent in amplitude and rate, but otherwise be continuous for an observation period lasting from 2 to 6 hours. If the animal becomes restless during the observation period the hunger contractions become irregular and may cease altogether, but this is probably due to splanchnic inhibition, and cannot be regarded as a spontaneous cessation of the hunger contractions.
This type of hunger contractions seems to be present only in young and vigorous individuals in excellent physical condition. Similar contractions were observed in man, but less frequently than in our young and vigorous dogs. From observations on man, it is certain that the hunger sensation is practically continuous during these contractions.
The hunger contractions designated as type III constitute virtually an incomplete tetanus of the stomach. This tetanus is characterized by periods of strong and relatively persistent tonus on which are superimposed a series of rapid contractions. The duration of these rapid contractions averages 12 to 15 seconds. These contractions are evidently analogous to the 20-seconds rhythm in man. These tetanus periods vary in length from 1 to 10 minutes. In prolonged starvation they may last much longer. In moderate hunger they are interspersed between groups of the type II rhythm.
This description of the gastric hunger contractions in dogs is based on observations on more than fifty individuals. The shortest observation period on each animal was two weeks, the longest five months with records taken, on the whole, every third day. The data should therefore be typical. The three types of contractions may be observed in the same dog on different days, or type I may obtain for a few days, and then be superseded by type II, etc. As a general rule type I predominated in some of the dogs and types, II and III in others. Some of the tracings also disclose what may be termed transition stages. Thus, near the end of a contraction period of type I the rapidity of the contraction may approach that of type II, and occasionally the individual contractions of type II will for short periods slow up to such an extent that they parallel type I. This is to be expected, since the types of the hunger contractions seem to vary with the degree of gastric tonus, and this tonus may vary considerably during a single observation period. It is also to be noted that the hunger contractions may occasionally be feeble, irregular, or practically absent for at least 2 to 4 hours at a time in dogs that are seemingly in good condition. And this is usually the case if the dogs are in poor condition from any cause.
The credit of discovery of the rhythmical contractions of the empty stomach in dogs belongs to Boldyreff, but his account of the rhythm is incomplete and partly misleading. According to Boldyreff the contractions always come in groups of 20 to 30 minutes' duration, and during the i 1/2 to 2 1/2 hours' intervals between these groups in which the stomach is completely quiescent. The contractions observed by Boldyreff were evidently short and feeble periods of the type I contractions, but the duration of the interval between the contractions given by Boldyreff is on the whole much greater than that shown in my series. Boldyreff evidently never obtained the rhythm of types II and III in his animals. The difference in the results of Boldyreff and our own are probably due to (1) the condition of the animals, (2) the method of handling the animals, and (3) the method of registering the stomach contractions. Boldyreff used the classical silver cannula for the gastric fistula. This depresses the stomach. All the dogs had in addition to the gastric fistula (fundus) also duodenal, pyloric, pancreatic, or hepatic fistulae. His dogs were therefore subjected to much greater disturbance of digestion and metabolism than is the case of a simple fistula of the fundus as prepared by me. As the dogs were not in the best of condition, it is not surprising that they showed only the feeble rhythm of type I. But it seems likely that forcing the dogs by mechanical means to lie or stand in one position for 6 to 12 hours at a time is also partly responsible for the brevity of the contraction periods and the length of the intervening periods of quiescence. It is my experience.that dogs thus treated become restless, and restlessness always is accompanied by gastric inhibition, probably through the splanchnics. When the dog is allowed to make himself comfortable in the lap of an attendant he lies quietly and usually without any restraint. This condition is certainly more nearly normal.
The tracings published by Boldyreff do not show the respiratory intragastric pressures, nor do they indicate the slightest variations of the gastric tonus during the observation periods. His method of registration was therefore not delicate enough to detect small variations in the intragastric pressure. It would seem, however, that his method ought to have recorded the type II contractions, if they had been present in his dogs.