During the early years of our investigations on the nutrition of rats a number of our experimental animals showed on necropsy the presence of calculi in the kidneys or bladder. These calculi ranged in number from one to a hundred or more, and in size from particles no larger than the head of a pin to large stones which filled the entire kidney, leaving only a thin wall of tissue surrounding the concretion. The number of such cases gradually diminished until during the last two years we have failed to find this condition among our rats. In view of these facts and the additional experience that none of our stock animals was ever found to be affected in this way, it became a matter of some interest to attempt to correlate, if possible, the appearance of these calculi with the diets on which the animals had been fed.
OSBORNE TB, MENDEL LB. THE INCIDENCE OF PHOSPHATIC URINARY CALCULI IN RATS FED ON EXPERIMENTAL RATIONS. JAMA. 1917;LXIX(1):32-33. doi:10.1001/jama.1917.02590280034011