[Footnote 36: _N.Y. Med. Record_, June 18, 1881, p. 679. Exposure to the air for a considerable period seems to be the agency chiefly relied upon for what may be called the dynamic modification of these microphytes. When cultivated in the depth of a liquid, so that air is excluded, they are supposed to acquire a habit of obtaining oxygen by decomposing organic substances, and thus act destructively upon the cell-elements of living bodies. Analogous differences have long since been observed in the study of fermentation between surface and sedimentary yeast.] In none of these cases is there reported any morphological change whatever in the bacillus (Grawitz) or micrococcus (Wood and Formad); the change in the effects noted, and, in the case of the micrococci of malignant diphtheria, the acquired capacity of reproduction through several generations, are all. 8. The immunity against subsequent attacks on exposure (similar to the protection given by vaccination) continues to be without full explanation upon any theory. But it is especially difficult to reconcile it with the hypothesis of the infection being caused by, and dependent upon, the presence of peculiar microphytes. Why should not these, whether as parasites or as poisons, always produce the same effects? 9. The view entertained by Thorne, Wood, and Formad, that a common benignant affection, such as ordinary sore throat, may be converted into a violent infectious disease--_e.g._ malignant diphtheria--by modification of innocent micrococci into those with lethal characters, through local or bodily conditions, is sufficiently contravened by the great frequency of such conditions compared with the decided relative rarity of such malignant epidemics or endemics.