Randle S, Sober H, Kohler G. J. Nutr. 1940. 20:459-466
Guinea pigs were fed on winter milk plus various supplements. Those fed on a supplement rich in the grass juice factor (rye grass) showed strong growth.
Various plants were assayed for the grass juice factor. Based on average weight gain in guinea pigs the best sources of this growth promoting substance were dehydrated cereal grass (cerophyl), rye grass, young white clover, peas, pea shells, cabbage, spinach. Cereal grasses are an excellent source of the factor but the amount present varies
with the age of the plant.
It was also noted that the amount of grass juice factor in plants varied according to the age of the plants. Young, smaller plants were very good sources of grass juice factor when compared with older matured plants.