It is this characteristic of non-transmissibility from mammals to birds, and _vice versa_, which forms the chief difference between the two kinds of tuberculosis. Strauss failed in his endeavor to inoculate a fowl with tuberculosis by injecting fifty kilogrammes of tuberculous human sputa, whereas the fowl, absolutely impervious to human tuberculosis, became infected when treated with a very slight quantity of the avian tuberculosis. The guinea-pig, so sensitive to the human microbe, presented encysted abscesses when treated with the virus of birds; it dies of cachexia, but never, as far as the naked eye can discern, of generalized tuberculosis. Rabbits are more sensitive to the avian infection. Dogs are absolutely refractory. The monkey, so delicate in our climate, and which almost invariably perishes from tuberculosis, is uninjured by inoculation from avian virus. The parrot is a remarkable exception to the general rule; it is the only bird which resists avian tuberculosis, while, on the other hand, it is sensitive to that of man. Such facts as these irrefutably differentiate the two kinds of tuberculosis. [H] _Tuberculosis of Birds._ _Tuberculosis of Mammals._ Aspect of Extreme softness on Human tuberculous cultures. glycerine jelly or growths are adherent, on serum. hard and difficult to break up even with a strong platinum wire on glycerine jelly as well as on serum. Medium of Transferred from a Cultivation more difficult. cultures. solid to a liquid medium the bacillus grows rapidly, having the appearance of rounded grains. Temperature. Develops at a Ceases to develop at temperature of 45° C. temperatures under 41° C. Odor. Somewhat sour. More subtle and fresh odor. Duration. Takes longer to develop, Is with difficulty generated and may remain again at the end of six for a year or months. At the end of thereabouts. eight or ten months loses its vegetable character. Seat of the In animals usually In the lung, generally in tubercles. on the liver, the men, and in certain animals; spleen, the intestines, in the spleen, the and the peritoneum. liver, and the glands in rabbits and guinea-pigs.