CHAP. VIII.

Influence of the Motion of the Air

THE motion of the air, without regard to its state of humidity or dryness, acts on the animal economy, by insensibly increasing the perspiration, and depriving it of its caloric, in a greater or less degree, according to the rapidity or slowness of its motion; a circumstance which should be carefully observed. The wind, and a strong current of air, therefore, demand attention; it is necessary that we explain their action on the economy, as it is modified by dress, habitation, or shelter; and this we shall endeavour to accomplish, by relating an experiment. Later on we shall draw consequences from the prolegomena we bring forward.

The state of perspiration varies so frequently, that it would be impossible to say any thing precise respecting it; these fluctuations are ascribed to the continual motion of the atmosphere, acting imperceptibly on the animal

economy.

In order to be perfectly acquainted with the influence of the air upon animals, Mr. Edwards suspended a certain number of frogs near a window that was kept shut, where they were sheltered from external air; and in the same apartment, near an open window, he hung some more

of these animals, so that as the air came into the room, it rushed on the latter, and only reached the former, after it had gone through the whole apartment. In this double experiment, even when the air was calm, the difference in the perspiration was very striking; the frogs near the open window, perspired twice as much as those that were at the opposite side of the room, and in a still greater degree, according to the intensity of the wind.

These experiments shew that when a great number of children are assembled together, if the windows are not kept shut, it may prove prejudicial for those who sit too near an open window or door. In most hospitals there are screens placed round the beds that are near the door, to shelter the patients from the wind, a plan which should be pursued in all schools.

Numerous experiments have decidedly proved, that if humidity does not entirely prevent perspiration, it diminishes it considerably; if it be suppressed, or interrupted for any length of time, the skin loses its secretive powers. The inhabitants of damp climates have generally lymphatic constitutions, enlargement of the glands, scrofulous and cutaneous diseases.

The incessant motion of the earth, the stars, and the sea, keeps the mass of gas which surrounds the terrestrial globe, in continual agitation; the atmosphere, therefore, is never perfectly calm. The air is either damp or dry, according to the re

gions it traverses; and these great meteorological phenomena, subject man to divers vicissitudes, as sudden changes of temperature are extremely prejudicial to the constitution. Merely going from a warm to a cold room, suffices to disturb the functions of the skin, as the body may not then be in harmony with the surrounding physical agents. A due attention to this fact, so essential to the health, cannot be too earnestly impressed on the minds of those who have the charge of young females.

The density and thickness of the air are not the only qualities of a healthy atmosphere; it would be unfit for human development without other fluids, as caloric, light, electricity; thus, the human economy is in contact with all the physical agents of nature, and cannot exist without them. After having examined the different properties of air; its action on organized bodies, and principally on man, we shall pursue our study on the other physical agents, requisite to the development of the animal economy.

CHAP. IX.

On Heat and Cold.

THE opinion of many ancient philosophers, that heat was the soul of the world, does not surprise those who are acquainted with its different powers. In its natural state, caloric is found in all organized bodies, whose particles are separated by the presence, or united by the absence of heat. Caloric acts in a different direction to the laws of attraction, discovered by Newton. When in contact with our organs, it produces a sensation termed heat.

One of the most striking effects of heat is shewn in its action on water; which when deprived of its caloric, is condensed, and turned into ice; while, on the contrary, a certain degree of heat converts it into vapour. If caloric has so much power on an inert body, how much greater influence must it possess on living creatures, though they be endowed with a temperature which scarcely varies. Caloric dilates nearly all bodies.

The quantity of caloric contained in bodies, is called their temperature. The atmospheric temperature, whatevermay be its degree, has always an influence on the animal economy; this influence is less observable in a variable temperature; but a very hot, or very cold climate modifies the whole constitution.

In hot climates the brain loses its energy; the inhabitants are effeminate and indolent, always seeking repose. In southern countries, idleness is the pleasure so well defined, by the Italian adage, il dolce far niente. In Asia, Turkey, Africa, fatally privileged for slavery, the natives seem to want even sufficient strength to break their chains; whilst in Europe, where the climate is temperate, a spirit of independence prevails, and is continually struggling against the oldest and best established institutions.

In warm climates, life is sooner consumed; puberty, the critical age, and even death is premature; one year, passed under the tropics, is equal to two spent in Europe. The slightest wounds are followed by spasms and tetanus ; muscular strength is in an inverse proportion to the sensitive faculties.

The temperature of hot climates is favourable to brain fevers and madness. In some countries heat is so intense, that it causes sudden death. Foaldo states that, in 1743, from the 14th to the 28th of July, eleven thousand women were found dead in the streets at Pekin.

In the summer months, diseases of the skin are more numerous, and contagion more frequent; this is the case in all warm climates.

But if excessive heat is to be avoided, a mild temperature may essentially benefit delicate constitutions, by assisting the development of weak organs, that are in a state of inactivity. Warmth,