5. That these microbes, microphytes, or mycrozymes act not as parasites, but as poison-producers, secreting a sort of ferment which is the specific morbid material (Virchow); or, when multiplying in excess of their food-material, they may die, and their dead bodies, like other decaying organic matter, may become poisonous. This possibility, although not distinctly suggested (so far as I know) hitherto, appears to me to be not unworthy of consideration. That the numbers of micro-organisms present have some important relation to morbid conditions has long since been inferred from familiar facts. 6. That they are not generators, but carriers, of disease-producing poisons; their vitality giving to the latter a continuance of existence and capacity of accumulation and transportation not otherwise possible. Briefly, the following is a summary of the most generally accepted classification of those microscopic organisms[21] whose rôle in the causation of diseases is now under discussion; chiefly following Cohn and Klebs: _Orders_: Hyphomycetæ, Algæ, Schizomycetæ. Hyphomycetæ, _genera_: Achorion, Tricophyton, Oidium. Algæ, _genera_: Sarcina, Leptothrix. Schizomycetæ, or Bacteria, _genera_: Micrococcus, Rod-bacterium, Bacillus, Spirillum.[22] [Footnote 21: For further details concerning these the reader is referred to the works of Magnin, Belfield, and Gradle on _The Bacteria_, and on the _Germ Theory of Disease_.] [Footnote 22: Cohn also separates vibrio and spirochæte as genera distinct from spirillum. They may, however, be regarded rather as species of that genus. Some recent authors included bacterium and bacillus under one genus, bacillus; against which simplification there seems to be no valid objection.] Micrococci (Sphærobacteria of Cohn) are asserted (under certain conditions) by Letzerich, Wood, and Formad[23] to be causative of diphtheria; Ogston has found them in ordinary pus; Rindfleisch, Recklinghausen, Waldeyer, Birch-Hirschfeld, and others report them to be always present in the abscesses of pyæmia; Buhl, Waldeyer, and Wagner state their occurrence in intestinal mycosis; Eberth, Köster, Maier, Burkhardt, and Osler, in ulcerative endocarditis; Orth, Lukomsky, Fehleisen, and Loeffler, in erysipelas; Coats and Stephen in pyelo-nephritis; Friedländer, in pneumonia; Eklund (_Plax scindens_) in scarlet fever; Keating[24] and {142} Le Bel, in measles; Leyden and Gaudier, in cerebro-spinal meningitis; Carmona del Valle, in yellow fever; Prior, in dysentery; Gaffky, Leistikow, Bokai, and Bockhardt, in gonorrhoea;[25] besides other similar observations by numerous writers. [Footnote 23: _Bulletin of National Board of Health_, Supplement No. 17, Jan. 21, 1882.] [Footnote 24: _The Medical News_, Philadelphia, July 29, 1882.] [Footnote 25: Sternberg's careful experimentation seems to show the identity of Neisser's gonococcus with the Micrococcus ureæ, commonly found in decomposing urine.]