Besides the micro-organisms everywhere grouped as bacteria, there are other minute organisms which have also the power of engendering pus. One of these is the ray fungus, known as the _actinomycis_, which causes the disease known as lumpy jaw or actinomycosis. Suppuration is always a concomitant of the advanced lesions of this disease, and, while it may be in many instances a mixed infection, it is not necessarily so. Moreover, the pus produced under these circumstances contains minute calcareous particles which are pathognomonic, by which a diagnosis can sometimes be made off-hand. Besides these fungi, others, belonging rather to the class of vegetable molds, which are yet pathogenic for human beings, may be occasionally met with under these circumstances--_e. g._, _the fungus of Madura foot_, the _leptothrix_, and other molds from the mouth, while the different varieties of _aspergillus_ may be found in pus about the ear or even in that from the brain. PROTOZOA. The protozoa have the power of producing, if not absolute ideal pus, something so nearly resembling it that we may include them among the facultative pyogenic organisms. The best known of these protozoa are the _amebæ_, which are met with in the intestinal canal in some countries, occasionally in the United States, especially as the exciting causes of a peculiar type of dysentery often accompanied by abscess of the liver. In these abscesses the amebæ are found, and no other organisms. Another group of the protozoa, known to biologists as the _coccidia_, are also capable of causing pus formation, more particularly in some of the lower animals. Numerous other parasites, belonging higher in the animal kingdom, are undoubted exciters of pus formation, though it is not necessary to lengthen the list beyond those already mentioned. [Illustration: FIG. 9 Blastomycetic pus (fresh). × 1000. (Gaylord.)] Protozoa have recently been established as the active agents in the production of smallpox and probably also of scarlatina. They have been seen so generally in and around cancer cells as to make it extremely probable that cancer is a protozoan infection. In syphilis also they are found as the _spirochetæ_, now regarded as its cause. Protozoa are as ubiquitous as bacteria, but their recognition is as yet more difficult, as but little is known of them. The numerous stages through which they pass in completing their life cycles only complicate the subject, while the difficulties encountered in cultivating them are still to be overcome. As we become more familiar with them we shall more frequently find them to be pathogenic organisms. CLINICAL CHARACTERISTICS OF PUS FROM DIFFERENT AGENCIES. _Staphylococcus._--Dirty white, moderately thick, with sour-paste odor. _Streptococcus._--Thin, white, often with shreds of tissue. _Colon Bacillus._--Thick, brownish, with fetid odor, or thin, dirty white, with thicker masses. _Micrococcus Lanceolatus._--Thin, watery, greenish, often copious.