If we view the progress of this terrific malady, as it tends to disorganise society wherever it shows itself, as it causes the destruction of human life on an extensive scale, or as it cramps commerce, and causes vast expense in the maintenance of quarantine and cordon establishments, no subject can surely be, at this moment, of deeper interest. It is to be regretted, indeed, that, in this country, political questions (of great magnitude certainly), should have prevented the legislature, and society at large, from examining, with due severity, all the data connected with cholera, in order to avert, should we unhappily be afflicted with an epidemic visitation of this disease, that state of confusion, bordering on anarchy, which we find has occurred in some of those countries where it has this year appeared. Were this letter intended for the eyes of medical men only, it would be unnecessary to say that, during epidemics, the safety of thousands rests upon the solution of these simple questions:--Is the disease communicable to a healthy person, from the body of another person labouring under it, either _directly_, by touching him, or _indirectly_, by touching any substance (as clothes, &c.) which might have been in contact with him, or by inhaling the air about his person, either during his illness or after death?--Or is it, on the other hand, a disease with the appearance and progress of which sick persons, individually or collectively, have no influence, the sole cause of its presence depending on unknown states of the atmosphere, or on terrestrial emanations, or on a principle, _aura_, or whatever else it may be called, elicited under certain circumstances, from both the earth and air?--In the one case we have what the French, very generally I believe, term _mediate_ and _immediate_ contagion, while the term _infection_ would seem to be reserved by some of the most distinguished of their physicians for the production of diseases by a deteriorated atmosphere:--much confusion would certainly be avoided by this adoption of terms.[1] Now it is evident, that incalculable mischief must arise when a community acts upon erroneous decisions on the above questions; for, if we proceed in our measures on the principle of the disease not being either directly or indirectly transmissible, and that it should, nevertheless, be so in fact, we shall consign many to the grave, by not advising measures of separation between those in health, and the persons, clothes, &c., of the sick. On the other hand, should governments and the heads of families, act on the principle of the disease being transmissible from person to person, while the fact may be, that the disease is produced in each person by his breathing the deteriorated atmosphere of a certain limited surface, the calamity in this case must be very great; for, as has happened on the Continent lately, cordons may be established to prevent flight, _when flight, in