actinomyces in producing no pigment and forming white raised colonies on agar. Probably there are several conditions in actinomycosis, as in mycetoma, bearing a general resemblance to each other, but differing slightly according as they are produced by different species of streptothrix.
Morbid anatomy.— On cutting into a mycetomatous foot or hand the knife passes readily through the mass, exposing a section with an oily, greasy surface, in which the anatomical elements in many places are unrecognizable, being, as it were, fused together, forming a pale, greyish-yellow mass. The bones in parts have entirely disappeared; where their remains can still be made out the cancellated structure is very friable, thinned, opened out, and infiltrated with oleaginous material. Of all the structures the tendons and fasciæ seem to be the most resistant.
The most remarkable feature revealed by section is a network of sinuses and communicating cyst-like cavities of various dimensions, from a mere speck to a cavity an inch or more in diameter. Sinuses and cysts are occupied by a material unlike anything else in human morbid anatomy. In the black varieties of mycetoma this material consists of a black or dark brown, firm, friable substance which, in many places, stuffs the sinuses and cysts; manifestly it is from this that the black particles in the discharge are derived. In the white varieties the sinuses and cysts are also more or less stuffed with a white or yellowish roe-like substance, evidently an aggregation of particles identical with those escaping in the corresponding discharge. The black substance, which can be readily turned out, is moulded into truffle-like masses ranging in size from a mere grain to a small apple, according to the capacity of the cysts or sinuses containing it. The roe-like particles in the white varieties are held together by a softer, cheesy -looking material. The sinuses and cysts occupy the bones, muscles, or fasciae indiscriminately; they are found principally in the fat and the connective tissue. They are lined with a smooth membrane, adherent when in the soft tissues, but capable of being enucleated when in the bones. Some of the cysts do not communicate with sinuses; most of them, however,
