(4) The appropriateness of the food is a very important factor in the health of an animal under captive conditions. Diet lists are made up by officials largely according to the known habits and general physiology of an animal, but the food offered can at best only approximate what the wild beast obtains for himself. It does not follow because a selected diet may seem to provide all the elements contained in the food available under natural conditions that it actually does so, especially since we are aware that some essential food factors, known under the term vitamins, are necessary to best development. These substances vary in closely similar foods, and seem to be higher in simple natural foods than in prepared diets. We have seen in this Garden that the inorganic constituents must be correctly represented in the food, else degenerative osseous condition may develop. Inappropriate diet may express itself at once after the receipt of an animal, by its sickness or death, or after some time in the development of chronic tympanites, chronic intestinal catarrh or bony deformities. (5) The physical condition of food is a matter of no small moment. The taking of soft food in large quantities especially by herbivorous animals, permits too short a sojourn in the gastric fundus and is often followed by pyloric and duodenal disease. Too firm food may pack the rumen, fundus or proventricle as the case may be, and be succeeded by distention of these parts and catarrh of the pyloric and intestinal area. The effect of foreign bodies mixed with food is difficult to evaluate unless of course they be of such a nature (pointed metal and the like) as directly to traumatize the mucosa. Many birds and mammals come to autopsy with a relatively large number of stones and small sticks in the stomach without any distinct evidence that they have been hurt thereby. In the bird the stones may be so large and numerous as to leave little room for food, or small enough to pass out into the intestine where they undoubtedly may pave the way for bacterial action. Smoothly polished pebbles in small quantity seem to have little effect in mammals. Hair balls are not common and unless of large size are apparently unimportant. Considerable sand mixed with food has a distinctly irritating effect. It is perhaps best known as a chronic gastric disorder of horses; we have seen it in zebra.