Almost all individuals are intensely Gram-positive, and show regularity of outline. All strains show involution form, exhibiting vacuoles, and often show empty cell membranes. The latter are Gram-negative, and vary greatly in both dimensions as well as in form. All strains show tendency to chain formation, some being arranged in chains of six to twenty-five segments, which may contain both Gram-positive and Gram-negative individuals. Type B exhibits Gram-negative spherical bodies varying from 0.25 µ to 1 µ in size, adhering to the sides of some of the Gram-negative individuals. _In Whey._—In this medium there is a marked tendency toward degeneration and involution. In the early stages of incubation, at 100° to 112° F., the bacilli are uniform in size and intensely Gram-positive; in succeeding stages the irregular, vacuolated, inflated, and ruptured forms predominate. Between the eighteenth and twenty-fourth hours of incubation at 112° F. the strains of type A develop oval to kidney-shaped nodules attached to a stem extending from the cell substance. As the incubation is prolonged these nodules increase in size, often measuring 1 µ to 2 µ in length; this nodule formation occurs at the expense of the cell protoplasm, and appears to be a marked characteristic of growth in whey. Cultures of type B do not form nodules or clubs, but small spherical bodies more or less securely attached to the cell wall are seen. Again, type A assumes the form of small bacilli in chains, while type B strains develop to a greater length and exist almost exclusively as single isolated forms. True branching has been observed in strains of type B. _In Milk._—In milk there is a tendency to thread-formation consisting of four to ten segments in the case of type A, while type B shows longer and more curved forms. With increasing age of the culture there also appears to be increase in the length of the organisms. All strains are non-motile, non-sporogenous, and non-capsule-forming. _Staining Reactions._—All strains are readily stained by the usual aniline dyes. _A. Gram's Method._—Young individuals give an intense reaction with this stain; old bacilli are easily decolourised, and degenerate forms are always Gram-negative, while single individuals have been observed which showed gradation from one pole of the cell to the other.