It is further of interest to point out, in the light of our present knowledge that if the rat had been susceptible to the disease scurvy, these experiments would both have ended in failure and no possible explanation would have been apparent, for in both cases the series of diets employed were lacking in the anti-scorbutic substance which is essential for the normal nutrition of certain species such as man, monkey and guinea pig. Fortunately for progress in this branch of science, the rat is immune to scurvy, because he can synthesize the anti-scorbutic substance from other complexes in the food. For the demonstration of the nature of scurvy and its relation to faulty diet, it was necessary to employ another species of animal, the guinea pig, as an experimental subject.