Rabbits were caused to inhale known numbers of virulent bovine tubercle bacilli as separated cells in droplet nuclei.

For approximately 5 weeks after infection the growth of the bacilli and the response of rabbits to their growth was homogeneous; i.e., all reacted in the same way and to the same degree.

After 6 weeks individual differences in the rate of progress of the initial tubercles and of the infection as a whole became evident. These variations in the response seemed to be influenced by the number of initial tubercles and by the number of bacilli found in the lesions.

It is concluded that, as evidenced by the homogeneous phase of infection, rabbits do not differ in their resistance to initial growth of bovine tubercle bacilli. However, the later, heterogeneous pattern of response suggests that these animals vary widely in their capacity to acquire resistance.

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