“In a country which keeps up its population at a certain standard, if the average number of marriages and births be given, it is evident that the average number of deaths will also be given: and to use Dr. Heberden’s metaphor, the channels through which the stream of mortality is constantly flowing will always convey off a given quantity. Now, if we stop up any of these channels, it must be perfectly clear that the stream of mortality must run with greater force through some of the other channels: that is, if we eradicate some diseases, others will become proportionally more fatal.” “Dr. Heberden, (says Malthus) draws a striking picture of the favorable change observed in the health of the people of England, and greatly attributes it to the improvements which have gradually taken place, not only in London but in all great towns; and in the manner of living throughout the kingdom, particularly in respect to cleanliness and ventilation. But these causes would not have produced the effect observed, if they had not been accompanied by an increase of the preventive check; and probably the spread of cleanliness, and better mode of living, which then began to prevail, by spreading more generally a decent and useful pride, principally contributed to this increase. The diminution in the number of marriages, however, was not sufficient to make up for the great decrease of mortality, from the extinction of the plague, and the striking reduction of the deaths from the dysentery. While these, and some other diseases became evanescent, consumption, palsy, apoplexy, gout, lunacy and the small-pox became more mortal. The widening of these drains was necessary to carry off the population which still remained redundant, notwithstanding the increased operation of the preventive check, and the part which was annually disposed of, and enabled to subsist by the increase of agriculture.” Mr. Malthus then adds: “For my own part, I feel not the slightest doubt, that if the introduction of the cow-pox should extirpate the small-pox, and yet the number of marriages continue the same, we shall find a very perceptible difference in the increased mortality of some other diseases. Nothing could prevent this effect but a sudden start in our agriculture; and should this take place, which I fear we have not much reason to expect, it will not be owing to the number of children saved from death by the cow-pox inoculations, but to the alarms occasioned among the people of property by the late scarcities, and to the increased gains of farmers, which have been so absurdly reprobated. I am strongly, however, inclined to believe, that the number of marriages will not in this case remain the same; but that the gradual light which may be expected to be thrown on this interesting topic of human inquiry, will teach us how to make the extinction of a mortal disorder, a real blessing to us, and a real improvement in the general health and happiness of the society.”