Growth and Reproduction on Synthetic Diets. Part I

THE use of synthetic diets in nutrition experiments occupies a prominent place in modern research. For many years American workers have used what may be termed "semi-synthetic" diets in which such constituents as rolled oats, milk powder, etc., have formed a large bulk of the food, but experiments with true synthetic diets are not so numerous. It is of great importance to the nutrition worker to have a good standard synthetic diet, but at the present time such a food is not available. Various workers claim normal growth for animals on synthetic diets, but no control curve is given [e.g. Reader and Drummond, 1925]. In many instances the growth curve of Donaldson [1924] is taken as the standard, and it is quite true that rats on synthetic diets frequently show better growth than this, though not nearly so good as on a mixed diet of natural foods. The recent work of Osborne and Mendel [1926] shows that an improvement in the diet of the rat leads to a better rate of growth. These workers also found that the best growth was obtained on synthetic diets plus small additions of " natural foods," e.g. lettuce or liver. This obviously suggests that our synthetic diets are by no means perfect, and research work has yet to discover a synthetic diet which will produce as good growth as does the ordinary mixed diet of natural foods. Sherman and Campbell [1924] found that increasing the proportion of milk in an already adequate diet led to improved nutrition. Similar progress in true synthetic diets is badly needed. Mitchell [1922] added agar-agar to a synthetic diet and found that this led to the females breeding and rearing young, when they had previously failed. She suggests that bulk in the diet is a factor of importance. Previous work of the author [Hartwell, 1925, 2] also shows that the usual synthetic diets failed in this respect, and a method was described for overcoming this difficulty in another way. It seems useless to discuss the amounts of the various vitamins necessary for normal growth when we are using a diet which in itself only permits submaximal growth. Therefore, at the present time, it appears to be of vital importance for us to have a true synthetic diet which will provide for growth equal to that produced on ordinary mixed food. The experiments described in this paper were started in the hope of obtaining an improved synthetic diet.