In all animal experiments it is of the greatest importance that the bacteria be known which may interfere in the experiments through spontaneous infection (often liable to be induced by the injection) from the animal’s own flora, as well as the greater susceptibility of previously diseased animals (Nastjukoff). It would appear from the results of Bruschettini and Cornil and Chantemesse in the early days of the influenza bacillus, and those of Lamb and Brannin in their recent study, that these authors did not seriously consider the spontaneous infection of guinea pigs and rabbits with B. bronchisepticus or the bacillus of rabbit septicæmia, both morphologically, very similar to B. influenzæ. Rosenow in his experiments with streptococci from cases of influenza has also apparently failed to realize the importance of the lung lesions produced by the B. bronchisepticus in guinea pigs as reported by Theobald Smith, myself and many others. Parker has found a filterable poison from the influenza bacillus which developed rapidly (6 to 8 hours) in a special heated blood broth medium, deteriorated rapidly even in the cold, and killed rabbits in quantities of 2 c.c. in from 1 to 3 hours. Rabbits could further be immunized against this poison, and their sera protected other rabbits against fatal doses. This is the first time that a true powerful toxine has been obtained. Couret and Herbert obtained toxine from B. influenzæ in Avery’s oleate broth. Huntoon and Ross also clearly demonstrated toxine production by this organism so that it would appear, with this confirmation, that the B. influenzæ can be definitely classed among the toxine producers. Toxemia being the most striking clinical characteristic of influenza, we have in these findings very strong evidence of the etiological importance of this hemophilic bacillus to the disease. A very interesting observation was made by Latapie that the serum of a goat immunized against influenza bacillus is toxic if it is used shortly after the injection of the microbes, but that this toxicity is absent three weeks after the last injection. It would appear to me that the evidence of a filterable virus from the secretions of the respiratory tract does not eliminate the very probable toxine from such materials. The production of toxine by this organism probably depends, as is the case with very many of our toxine formers, on the most favorable combinations of conditions. That it is not readily formed in artificial cultures, or that it is very unstable if formed, is evidenced by the frequent failures of a great many workers. It has been suggested that different symbiotic conditions in the respiratory tract determine the amount of toxine produced. Huntoon found a high toxine production in mixed cultures with streptococci. This, however, does not appear to be necessary, as there is ample evidence of severe toxemia from pure infections with B. influenzæ in various parts, such as the accessory