when the dog is shown food but does not eat it. This " appeitite secretion " is large in quantity, and as powerful in quality as that produced by true feeding. But this secretion does not last more than two hours, if no food is received in the stomach, though it can be reproduced by the same stimuli as before. On the other hand, if food be introduced into the stomach unknown to the dog, as when he is asleep, and without awakening appetite, the secretion is from the first small in quantity but lasts for a much longer time. Natural secretion is the sum of both effects. Different kinds -of food vary much in their power to excite secretion. In a dog whose cesophagus is intact meat, milk, and bread are at different times given in quantities representing the same ,equivalent of albuminoids. The meat produces a free flow, the milk a scanty flow, the bread a scanty flow of very powerful juice. The acidity of normal gastric juice does not vary with the pepsin, but remains the same unless neutralised by mucus. Food introduced unawares into the stomach also produces a variable secretion. Bits of meat excite secretion to a certain extent, but egg albumen, bread, and milk not at al 1. All meat extracts produce the effect of meat. Mechanical irritation produces no secretion whatever. Experiments have proved that in meat there are some bodies already existing which provoke secretion, and that similar bodies may be produced in the other foods by the act of digestion itself, so th.at once started as by the " appetite secretion," the process is kept up. Both stomach and pancreas are under the control of nerves. To both the vagus certainly, and probably the sympathetic too, acts as a secretory nerve. Inhibitory fibres likewise exist, which run in the vagus. " Appetite secretion" is excited through the vagus, and stops directly if during the secretion the vagus be severed. Contact secretion, from the food in the stomach, is likewise a reflex act, and is not due to any direct influence upon the peptic glands. Pancreatic secretion studied by a pancreatic fistula shows ;eimilar variation in quantity and quality. It is little if at all affected by appetite. Its chief excitant is the acidity of the ehyle, which acts reflexly through the duodenal mucous membrane. Starch excites pancreatic secretion no more than water, but fat has a marked effect. Yet the little pancreatic juice that is produced by feeding with bread has a much greater amylolytic power than that produced by meat feeding. Fat produces both a considerable amount of juice, and a juice that has strong fat-splitting power. We have written enough to show that Dr. Pawlow's lectures mark a great advance in the physiology of digestion. It is, as we have said, a summing-up of many previous original papers to which rather than to the lectures those must turn who require the original material in large quantities. But by far the largest part-in fact for each of us all but a very small part-of scientific knowledge rests upon our belief in the trustworthiness of someone else, and these lectures are such as to command the credence and admiration accorded to the best work and the best workers alone.
K. Balfour, A. Bruce
British Medical Journal