The literature relating to periodical fevers contains nothing else so interesting as the very ingenious article of Dr. J. H. Salisbury, on the "Cause of Malarious Fevers," contributed to the "American Journal of Medical Science," for January, 1866. Unfortunately, while there is no evidence to controvert the statements of this article, they do not seem to be honored with the confidence of the profession,—not being regarded as sufficiently authenticated to form a basis for scientific deductions. Dr. Salisbury claims to have discovered the cause of malarial fever in the spores of a very low order of plant, which spores he claims to have invariably detected in the saliva, and in the urine, of fever patients, and in those of no other persons, and which he collected on plates of glass suspended over all marshes and other lands of a malarious character, which he examined, and which he was never able to obtain from lands which were not malarious. Starting from this point, he proceeds, (with circumstantial statements that seem to the unprofessional mind to be sufficient,) to show that the plant producing these spores is always found, in the form of a whitish, green, or brick-colored incrustation, on the surface of fever producing lands; that the spores, when detached from the parent plant, are carried in suspension _only in the moist exhalations of wet lands_, never rising higher, (usually from 35 to 60 feet,) nor being carried farther, than the humid air itself; that they most accumulate in the upper strata of the fogs, producing more disease on lands slightly elevated above the level of the marsh than at its very edge; that fever-and-ague are never to be found where this plant does not grow; that it may be at once introduced into the healthiest locality by transporting moist earth on which the incrustation is forming; that the plant, being introduced into the human system through the lungs, continues to grow there and causes disease; and that _quinia_ arrests its growth, (as it checks the multiplication of yeast plants in fermentation,) and thus suspends the action of the disease. Probably it would be impossible to prove that the foregoing theory is correct, though it is not improbable that it contains the germ from which a fuller knowledge of the disease and its causes will be obtained. It is sufficient for the purposes of this work to say that, so far as Dr. Salisbury’s opinion is valuable, it is,—like the opinion of all other writers on the subject,—fully in favor of perfect drainage as the one great preventive of all malarial diseases. _The evidence of the effect of drainage_ in removing the cause of malarial diseases is complete and conclusive. Instances of such improvement in this country are not rare, but they are much less numerous and less conspicuous here than in England, where draining has been much more extensively carried out, and where greater pains have been taken to collect testimony as to its effects.