day by day, predict results.  There is a fall of temperature that shall be known by experience to be sufficiently deep and prolonged to cause an increase of one death among those members of the community who have reached thirty years.  Then, rising by a definite rule, there have died sixty-four, in proportion to that one, of those who have reached eighty-four years.  This is sound calculation, and it leads to reflection.  It leads one to ask, what, if the law be so definite, are curative and preventive medicine doing meanwhile, that they shall not disturb it?  I fear that they hardly produce perturbations, and I do not see why they should; because, as the truth opens itself to the mind, the tremendous external change in the forces of the universe that leads to the result, is not to be grappled with nor interfered with by any specific method of human invention.  The cause is too general, too overwhelming, too grasping.  It is like the lightning stroke in its distance from our command; but it is widely spread, not pointed and concentrate; prolonged, not instantaneous; and, by virtue of these properties, is so much the more subtile and devastating.

At first it seems easy to explain the reason why a sudden fall in temperature should lead to an increase in the number of deaths, and it is to be admitted that, to a certain extent, the reason is clear.

ANIMAL POWER AT DIFFERENT PERIODS OF LIFE.

Without entering on the question whether heat is the animating principle of all living organisms, we may accept that in the evolution of heat in the body we have a measurement of the capacity of the body to sustain motion, which is only another phrase for expressing the resistance of the body to death.  For example, if we assume that a healthy man of thirty respires sufficient air per day to produce as much heat as would raise fifty pounds of water at 32 deg.  Fahr. to 212 deg.  Fahr., and if we assume that a man of sixty in the same temperature is only able to respire so much air as shall cause him to evolve so much heat as would raise forty pounds of water from 32 deg. to 212 deg., we see a general reason why the older man should feel an effect from a sudden change in the temperature of the air which the younger would not feel; and if we assume, further, that a man of eighty could in the same time produce as much heat as would raise only twenty pounds of water from 32 deg. to 212 deg., we see a good reason why the oldest should suffer more from a decrease of external temperature than the other two.  It is necessary, however, to know more than this general statement of an approximate fact; we ought to understand the method by which the reduction of temperature influences, and the details of the physiological process connected with the phenomena.  When a human body is living after the age when the period of its growth is completed and before the period of its decay has commenced, it produces, when it is