It has been shown that in a large group of rabbits inoculated intravenously with bovine tubercle bacilli the disease which follows resolves itself into two distinct phases. The first phase manifests itself in widespread diffuse lesions which subsequently regress. The mortality rate shows a rise and fall during this period, which have been correlated with the extent of lesions and with the changes in the blood cells. The duration of this phase is approximately 80 to 90 days. Following this period the mortality rate again rises and falls, during a period when all animals show lesions of a chronic nature. In an infected group the number of fatalities in the first phase is a function of the size of the dose. When the size of the dose and other conditions are held constant, a definite basis upon which to compare the reactions of treated animals is established.
Studies of the blood cells during the course of the disease show that the changes in these cells reflect the course of the lesions in the first phase when other signs are lacking and offer a valuable means of making an estimate of the state of resistance of the animal from time to time.
Studies of blood counts made on rabbits before their inoculation with tuberculosis were analyzed with regard to the relative longevity of the animals. It was found that those animals whose blood cells of various sorts deviated least from the modal value for the entire group survived longer than those animals whose counts were significantly high or low.