_Symbiosis._—The fact that other bacteria can bring to growth the influenza bacillus on media otherwise unsuited to its needs brings up the interesting problem of symbiosis, which is one of the most important characters of the influenza bacillus. Not only do other bacteria make possible the growth of B. influenzæ on media on which the influenza bacillus will not grow, but they stimulate a better growth on blood agar and other more or less favorable media. Grassberger first noted this stimulating character of other bacteria and described and illustrated the very large colonies of B. influenzæ which develop in the neighborhood of colonies of staphylococcus and other bacteria. Staphylococci killed by heat were found to have a similar effect. Meunier nicely described this phenomenon by using the term satellites for the circles of B. influenzæ colonies which develop about the colonies of other bacteria. A great number of workers have since noted this characteristic relationship between B. influenzæ and other bacteria, and occasionally have laid stress on its importance in the problems of the infections by the influenza bacillus. Allen particularly emphasized the probable importance of this in discussing the problem of carriers of B. influenzæ as sources of danger. There seems no doubt that this symbiotic relationship depends on so altering the hemoglobin products as to render them more readily available for the influenza bacillus. This is indicated by the fact that on various media containing hemoglobin, altered so that it encourages the growth of B. influenzæ, no such symbiotic stimulation can be demonstrated. This phenomenon is quite peculiar to this bacillus, distinguishes it from most of the other members of the group, and should be always determined before an organism is classed as B. influenzæ.