At first introduced to indicate the supposed results of pus and septic material respectively in the blood, these terms have come to represent the clinical phenomena which come from the introduction into a susceptible system of pyogenic and necrogenic microbes and their toxic products. Gradually different affections, which would have been included under the same general terms, came to be identified under specific names, and a number of these will be described as individual diseases—strangles, mouse and rabbit septicæmias, metritis, phlebitis, omphalitis, rouget, barbone, chicken cholera, septicæmia hæmorrhagica, etc.—yet a certain number have been left to be referred to under the generic terms, though respectively due to different microbes. _Distinctions between Pyæmia and Septicæmia._ _Pyæmia_ is a morbid condition characterized by the formation in different organs of multiple metastatic abscesses, dependent on the transference, in the blood stream, of infected clots, or particles containing pus microbes, and their arrest at distant points, so as to cause foci of suppuration commencing with the intima of the vessels. _Septicæmia_ indicates a general infection often by the same microbes, but showing its results in enlargement and blood engorgement of the spleen and lymph glands and necrotic foci of the liver, kidneys and other organs, but without the formation of multiple abscesses. The presence of the microbes in the different organs affected, shows that it is not due to the diffusion of the toxic chemical products alone, as at one time supposed, and the lack of abscesses appears to be due to the absence of clots or of modified and adhesive leucocytes or hæmatoblasts, which adhering to the epithelium of the vessels predispose to suppuration. The two conditions are, however, often combined, constituting what is known as _septico-pyæmia_. As in the occurrence of other infecting diseases, the condition of varying susceptibility must be taken into account, one individual, or one species resisting an inoculation which would be deadly to another. =Pyæmia.= _Causes._ The causation microbes are most commonly staphylococcus pyogenes aureus, or albus, the streptococcus pyogenes, and less frequently bacillus pyocyaneus, bacterium coli commune, and probably any pus producing microbe. Many conditions must however be accepted as contributing to the general infection. Inoculation on a mere abrasion or surface sore is not to be dreaded so much as if the virus is lodged _subcutaneously or in a deep wound_. The ready escape of the toxic products, the active leucocytosis which takes place in the granulations, and the action of the oxygen of the air are more or less protective in the exposed sores. The native _susceptibility of the subject_,—horse, ox,—conduces to the disease, while the insusceptibility,—bird—tends to obviate it.