And, nevertheless, gelatine contains a large quantity of nitrogen, which is one of the most powerful elements in nutrition; on the other hand, beef tea may be chosen as an illustration of great nutrient power in sickness, co-existing with a very small amount of solid nitrogenous matter. Dr. Christison says that "every one will be struck with the readiness with which" certain classes of "patients will often take diluted meat juice or beef tea repeatedly, when they refuse all other kinds of food." This is particularly remarkable in "cases of gastric fever in which," he says, "little or nothing else besides beef tea or diluted meat juice" has been taken for weeks or even months, "and yet a pint of beef tea contains scarcely ¼ oz. of anything but water,"—the result is so striking that he asks what is its mode of action? "Not simply nutrient—¼ oz. of the most nutritive material cannot nearly replace the daily wear and tear of the tissues in any circumstances. Possibly," he says, "it belongs to a new denomination of remedies."[5] It has been observed that a small quantity of beef tea added to other articles of nutrition augments their power out of all proportion to the additional amount of solid matter. The reason why jelly[6] should be innutritious and beef too nutritious to the sick, is a secret yet undiscovered, but it clearly shows that careful observation of the sick is the only clue to the best dietary. Chemistry has as yet afforded little insight into the dieting of sick. All that chemistry can tell us is the amount of "carboniferous" or "nitrogenous" elements discoverable in different dietetic articles. It has given us lists of dietetic substances, arranged in the order of their richness in one or other of these principles; but that is all. In the great majority of cases, the stomach of the patient is guided by other principles of selection than merely the amount of carbon or nitrogen in the diet. No doubt, in this as in other things, nature has very definite rules for her guidance, but these rules can only be ascertained by the most careful observation at the bed-side. She there teaches us that living chemistry, the chemistry of reparation, is something different from the chemistry of the laboratory. Organic chemistry is useful, as all knowledge is, when we come face to face with nature; but it by no means follows that we should learn in the laboratory any one of the reparative processes going on in disease.