After the salivary glands the most important structure for the digestion of starches in the animal economy is the pancreas. It was early evident, however, that the pancreatic secretion effected more than the conversion merely of starch into sugar. Its most important rôle, that of influencing the digestion and absorption of fats, was only recognized as the result of a classical observation of Bernard's upon the rabbit. He noticed that fat introduced into the digestive tract of a rabbit undergoes no change until it has advanced a considerable distance beyond the stomach. When fat is introduced into the dog's digestive apparatus a marked change {278} begins in it almost as soon as it leaves the stomach. At first this seemed very mysterious. Observations were made over and over again, always with the same result. There was evidently some important distinction between the intestines of the two animals. Careful investigation showed that the difference between the behavior of the fat in the rabbit and the dog was due to the presence or absence of the pancreatic fluid from the intestinal contents. In the dog the pancreatic duct which carries the secretion of the gland to the intestine empties into the intestine just beyond the stomach. In the rabbit the duct and its secretion empty into the intestine only some eight to ten inches below the intestinal orifice of the stomach. It is just beyond where the pancreatic duct reaches the intestine in both animals that the digestion of fat begins. This observation solved the seeming mystery of fat digestion, and at the same time made clear the importance of the pancreatic secretion in the general work of digestion.