Sir Gilbert _Blane_ considers, that the yellow fever may proceed from three remote causes, very distinct in their nature. The _First_, is that which consists in the exhalations of the soil, such as produce the endemic fevers in other countries and climates, and prevailing chiefly in autumn. The _Second_, is that which consists in foul air engendered on board of ships on long voyages, in circumstances of personal filth, and want of ventilation, frequently combined with hardships and privations, and is the same with those stagnated and corrupted effluvia of the living human body, which produce typhus fever. The _Third_ cause is that in which there is no suspicion of foul air, either from the soil, or from the living human body, but merely from circumstances of intemperance, fatigue, and insolation, affecting chiefly, and almost exclusively, new comers from temperate and cold climates.[195] The first of these, he says, may be distinguished by the appellation of the _Endemic_; the second, by that of the _Pestilential_, _Malignant_, or _Typhus Icterodes_; the third, by that of _Sporadic_.[196] And Sir Gilbert adds, that it has been for want of making this distinction, and from classing all these three under one head, that the endless and acrimonious controversies regarding contagion have arisen. There is not the least suspicion in any rational mind, that the endemic and sporadic species are contagious, this is only alleged with regard to the pestilential or typhus species; but it may be asked what proof there is that this last is specifically different from the other two? To this Sir Gilbert answers, that it is a matter of history; that besides the endemic and sporadic fevers prevailing at all times in the above-mentioned regions, there has occurred at various intervals of time, a raging epidemic,[197] which could be traced to the arrival of a ship or ships in the circumstances above recited, and at a season in which the ordinary malignant fevers do not prevail. To those engaged in researches upon this obscure subject we would farther recommend the perusal of a work lately published by that veteran in the cause, DR. JACKSON, on the subject of the Andalusian Fevers[198]; in which he examines the evidence in support of the supposed introduction of the yellow fever into Spain, and of its real or supposed propagation by contagion. The importation of the disease from a foreign country is credited by the authorities and mass of people in Spain, though the author thinks it has never been proved by evidence, or even brought to reasonable probability; the events of the year 1820 stripping the assumption of every claim to credence, as no attempt has been made to trace the disease, in that instance, to foreign origin. The belief universally obtains through Spain, that the disease is personally contagious; that is, capable of propagation from individual to individual, by contact or proximity; Dr. Jackson, however, considers