=Secondary Infection.=--Secondary infection means that after certain disturbances due to a primary infection, _i. e._, one of a given type, there occurs at some later period and from a distinct source another infection whose results may be more or less disastrous, and cause the case, at least for the time being, to assume a different aspect. We have an illustration of this in the case, for example, of primary tuberculosis with distinct infection of a number of lymph nodes, which, acting as filters, have caught in their tissue net a large number of tubercle bacilli that, lodging there, have produced the usual well-known results and have practically converted the infected nodes into granulomata. In these infected masses well-known changes, such as those which follow tuberculous infection--atrophy, caseation, calcification, etc.--may be occurring, when suddenly there comes infection of a _pyogenic_ type from another source, and suppuration of the granuloma is the result. It is possible even to have a _tertiary infection_, of which the following may be a hypothetical instance: Primary infection with scarlatina or measles, by which vital susceptibility is in some instances lowered; as the result of this, secondary tuberculous infection in an individual previously resistant; and, third, a suppurative infection, as above described. In contradistinction to these distinct events, separated by an appreciable, sometimes a considerable, length of time, we recognize a _mixed infection_, where two or more organisms are implanted at or about the same time. An illustration of this is seen in most cases of gonorrhea in which there is a synchronous attack made by the gonococcus, which is a specific microörganism, accompanied by staphylococci or streptococci, whose effect will complicate the case and make it assume a less particulate type of infection. Mixed infections may often occur in other ways, as syphilis and chancroid, chancroid and gonorrhea, etc. Most cases of mixed infection belong rather to surgery than to general medicine, and constitute an apparent violation of the rule to which physicians often point--that two distinct infectious diseases are seldom communicated or acquired at the same time. Nevertheless, the facts remain as above. =Terminal Infections.=--Terminal infections constitute an apparent paradox, perhaps oftener in medical than in surgical cases. Few people, as Osler has shown, die of the diseases from which they suffer. The final exitus is due to a more or less rapid infection which terminates life. These terminal infections are mainly due to a few well-known microbes, such as the streptococcus, staphylococcus aureus, pneumococcus, bacillus proteus, gonococcus, bacillus pyocyaneus, and the gas bacillus. In surgery such infections are, perhaps, most often seen in malignant lymphoma, diabetes, tuberculosis, syphilis, cancer, and in the so-called surgical kidney. BACTERIA OF PUS FORMATION.