the former case, because the ventilator is not now filled with hot air as before, but with cold, and which is pressed out by the elasticity of the heated air at the ceiling, not rising by its own specific gravity.

Now, as we pass with the ventilating register to intermediate points on the wall between these extremes, we shall find the effects correspondingly modified, the ventilator always receiving its supply from above the register, and leaving the cold air below.

It will thus appear that with both registers at the floor, the room will be most quickly and most thoroughly heated; and as we pass the ventilating register upward, we increase the body of undisturbed cold air. From this we infer, that if the only purpose of the air flues were to heat the room and maintain its temperature, the registers should both be placed at or near the floor, and if the ventilator is not so arranged, however well the room is heated, there will always be a stratum of cold air near the floor of the room, which will produce cold feet for those occupying it.

When steam pipes are used for heaters, there is no supply-pipe to furnish a current of hot air. The heater should be placed near the floor, where it will be constantly immersed in the cold air. A current of heated air arises from it toward the ceiling, while it is the center of a circle of surrounding currents of cold air passing up to be warmed. The air, as it rises, gradually expands out at the top of the room. As it gradually gives out its caloric, it sinks downward to make room for the lighter and warmer. Thus it continues to sink until again at the floor, when it again comes up to be warmed, and again rises to the ceiling. Thus the air continues to rise and fall, as it receives caloric, and distributes it, mixing and mingling with that about it, until the whole is of equal temperature.

With such a heater there is no need of a ventilating pipe in order to warm the room; there is no fresh air admitted, and hence no demand for exit, except to the extent of the expansion of the atmosphere in the room by the heat, which will easily be accommodated in any building not air tight.

To change the air of a room thus heated, the supply of cold air should be admitted near the heater, where it will be immediately warmed, and the ventilating register placed as in the case of rooms heated by furnaces.

The human body in a limited space of confined air, becomes selfdestructive, and an additional use of the ventilator is to carry away the poisons which the air receives from the occupants of our houses, and maintain its purity.

We will now consider what are these poisons, their mode of dissemination, and the means requisite for their elimination.

At the head of this list we will enumerate carbonic acid gas, which is, when respired, a deadly poison. The average amount of carbon daily consumed by an adult, in pulmonary and cutaneous exhalation, in the form of carbonic acid, is about 10.8 ounces, the skin eliminating about one-thirtieth of the amount. The specific gravity of this gas is 1.52, atmospheric air being 1. Hence, by its great weight, it will settle toward the floor of the room and mix with the cold air there.

The average amount of aqueous vapor daily exhaled from the lungs is from sixteen to twenty ounces, the quantity depending upon conditions not necessary now to consider. This is not pure water, but contains in solution carbonic acid, hydrogen, nitrogen, phosphorus and a considerable amount of albuminous substances in a state of decomposition. When exhaled, this vapor has a temperature of ninety-eight to one hundred degrees, and being lighter than the air in the room, will rise toward the ceiling, and diffuse itself with the atmosphere there.

The average amount of fluid daily lost by insensible perspiration may be stated at from two to three pounds, and almost any man occupying a comfortably heated room will add a pound or two to this by sensible perspiration. Nor is this pure water; besides the mineral salts which it holds in solution, it has a large amount of organic substances in a state of incipient decomposition. This, too, comes to the surface at the temperature of the body, and when liberated, will rise to the ceiling, and mix chiefly with the warm air there.

Besides these principal, there are other impurities in less amount, which emanate from the body, or necessarily occur from our habits of living. Among these may be mentioned small quantities of nitrogen, sulphuretted hydrogen, ammonia, the vapor of saliva and the fumes of various perishing substances which may be present. Most of these substances, from their low gravity, will seek the ceiling and mix with the warm air there.

It is not to be understood that the impurities indicated will not separate themselves in chambers as stated. The atmospheric currents kept up by the access and egress of the air, and other causes producing agitation, will more or less mix them through the whole body of the air in the room; but the greater quantity of each will find the places above assigned them.

fence it will be apparent that of the substances which should be

carried out of the chamber by the ventilating flues, one class will be found at the floor and the other at the ceiling.

Now if the ventilating register be placed at the floor, it will carry off the cold air and carbonic acid, but leave the atmosphere of the room freighted with the lighter exhalations above enumerated, which have no way of escape. If, on the other hand, the register be placed at the ceiling the hot air and lighter impurities will pass out of the room, leaving the shivering sufferers below with cold feet and breathing carbonic acid. If it be placed at any point between these extremes, it will remove neither class completely, but leave the room poisoned with all by its taking out the best air in it.

No single register can act at the two points where it appears from what has been stated, means of egress are most necessary; hence it is apparent there should be two-one at or near the floor to remove the cold air and carbonic acid, and one at or near the ceiling to afford exit for the lighter exhalations enumerated. The latter will, of course, allow the escape of a quantity of warm air, but as this can not be separated from the impurities to be eliminated, the waste can not be avoided. It may be closed until the room is warmed, and the size of the current afterward graduated according to the number of persons in the room, for reasons which are apparent.

The lower register has a double use—the elimination of the carbonic acid, and the removal of the colder air. It is through this channel that the chief current from the furnace to the roof is to be maintained, and upon its capacity should chiefly depend the supplydraft from the furnace, and the frequency of the change of the whole body of the atmosphere in the chamber. The upper register need not be so large as the lower, for two reasons, viz: 1st, the current through it is a very strong one, for the reason already stated; 2d, this current affords no aid toward heating the room, but rather retards it by carrying off the caloric; its only purpose is to separate the air, and should only be large enough to prevent the concentration of the lighter exhalations.

In assembly rooms the air needs more frequent change, as more persons are breathing it, and these points of exit should have corresponding dimensions.

I may also state here what was omitted at its proper place-that the supply-pipe from the furnace and the ventilating registers should always be placed at opposite points of the room, so as to compel the currents of air to traverse the whole chamber.

SPERMATOZOA.

BY W. H. LEMON, M. D., BRAZIL, INDIANA.

In prosecuting, recently, some microscopic researches in entomology, in behalf of the New Albany Society of Natural History, those tiny creatures led me away by their charming proportions as they descended into the infinitesimal world, until I found myself in a strange new field, in search of the entosthoblast of being-the nucleus of the nucleolus of life,

With a magnificent glass, having a power of near seven hundred diameters, which it is my good fortune to possess, I have been able to elicit many interesting facts; some of these pertaining to human spermatozoa, may not be wholly uninteresting to many of the profession. the more especially so, since the questions of excessive fécundity and sterility are so often forced upon us.

The ultimate forms of animate and inanimate organisms seem to merge so nearly into one as to need but the presence or absence of the same subtle agent to convert both into neither (original inorganic atoms) or vitalize the whole, to bestow at some future moment the distinctive elements that chain the germule to the animal or vegetable kingdom.

Certainly, the world of forms begin the monad. From the huge creations of the midæval age, the mammoth palm, and mastodons, to the veriest midge of the present day, all began being alike: at once a cytoblast and cell-birth, a spermatozoa.

The pollen of the plant, and the semen of the animal, may fecundate in the same mysterious manner; and at some future day we may be able to see a twin brother to our own spermatozoa in the fairy dust of flowers.

A very recent specimen of semen, when first placed under the glass, seemed a living but ill-defined mass of maggots, but which was soon resolved into a structure of something like cellular tela and columnar epithelium, floating in colorless liquor seminis, amid which sported multiplied thousands of very young tad-poles, or more exactly, wiggle-tails, like those of stale rainwater-spermatozoa. Embryo beings, eh? What becomes of them when they pierce the ovule, eh, again?

That they are individual vitalities, nothing is clearer. They possess all the requisites to constitute them such. They have distinct

forms; rest or move as they choose, and live or die independently. They travel in different directions-meet and pass each other. One will wriggle and lash his tail for hours on the same spot, while another drives past him with ease, making a journey at once, in about thirty seconds, across the entire field of the microscope-full the one thousandth part of an inch-a truly wonderful feat! They will show signs of consternation and alarm, and dodge from cell to cell like lizards hunting a place of safety. I have seen three and four packed in a single celule the one-four thousandth part of an inch in diameter. Thrown into the vagina, they are said to travel universally in the direction of their destination, the uterus and ova; but on the glass-slide there is the utmost confusion, save among those on the outer edge of the film under examination, whose heads are turned nearly always toward the center of the mass, caught, as it dries up, running for deep water. Is that instinct, volition, or what? As the school-boy has it, for the present, we will call it "what.”

They possess a body or head, neck and tail. The body or head is an elipsoid in shape, at one end of the longer axis of which is inserted the caudal filament through a ring or button that forms the neck. Their entire length will average about one-twelve hundredth part of an inch. The body is about one-tenth of this in length, and one-twelfth of it through the shorter axis; hence it is about onetwelve thousandth of an inch long, and less than one-fourteen thousandth of an inch thick. The neck is about one-twentieth of the body, and the tail with a thickness equal to about the one-one hundred and sixty-eight thousandth of an inch, has the wondrous length of one-twelve hundredth of an inch. These measurements vary much with the different physical conditions of the animalcule. While in the normal state, they have the life-like translucent fullness of very young fish; in dying, they shrink and blacken, presenting well-defined outlines. They show a clear spot in the center of the body, which, however, may not be owing to anything peculiar in their structure, but to a law of light.

Not all specimens of semen possess spermatozoa-some many, some few; and in some again they are dead: hence not all are capable of fecundating; for that power, beyond question, lies in and depends upon the vital spermatozoa. Healthy semen teems with them. In an average specimen, recently examined, I counted three hundred in the clear focal field of my glass, the one-ten thousandth part of a square inch.