Animal miasmata, like all other poison, become more active in proportion to the quantity which we imbibe. When, therefore, the air is stagnant, and when many individuals contribute their respective supplies of effluvia to vitiate it, the atmosphere necessarily becomes satured with the poison; and when inhaled, conveys it in a more virulent and concentrated state to the extensive and delicate surface of the lungs.
The collection of animal effluvia in confined places, is the source of the generation and diffusion of febrile infection: but when the miasmata are respired, in a diluted state, the ill effects which they produce, though slower in their operation, are equally certain. They, to a certain extent, pollute the fountain of life, and ultimately break down the vigour of the most robust frame; impairing the action of the digestive organs, engendering the whole train of nervous disorders, and rendering the body more susceptible of disease.
The lungs and the skin may equally become the means of introducing poisonous or infectious matter into the constitution. The venom of a poisonous animal, the matter of small-pox, and many other contagions, produce their influence through the medium of the skin. Infectious diseases are communicated by the reception of air in our lungs, impregnated with contagious matter. The influence of the constant respiration of air in any degree impure, is fully evinced in the pallid countenances and languid frames of those who live in confined and ill-ventilated places; and the health of all classes of society suffers precisely in proportion to the susceptibility of their constitutions, and according to the greater or less impurities of the air which they habitually respire.
Of the offensive nature of animal effluvia, the senses of every one who enters a crowded assembly, must immediately convince him. When, therefore, we reflect on the state of the air which we breathe in churches, theatres, schools, and all crowded assemblies; and when we consider the amount of the exhalations emitted by each individual, and the very offensive nature of those emitted by many; and when, on the other hand, we take into consideration the importance of air to life, and the great quantity of this fluid which we daily respire, we must be naturally led to the adoption of such measures as would secure in our private dwellings, as well as in our public buildings, a full and unintermitting supply of fresh atmospheric air.
It is curious to observe the influence of habit, in reconciling us to many practices which would otherwise be considered in the highest degree offensive. Thus, while, with a fastidious delicacy, we avoid drinking from a cup which has been already pressed to the lips of our friends, we feel no hesitation in receiving into our lungs an atmosphere contaminated by the breath and exhalations of every promiscuous assembly.
“Were once the energy of air deny’d,
The heart would cease to pour its purple tide
The purple tide forget its wonted play,
Nor back again pursue its curious way.”
The next Subject of Curiosity we shall consider, is, The Hair of the Head.
If we consider the curious structure, and different uses of the hair of our heads, we shall find them very well worth our attention, and discover in them proofs of the wisdom and power of God.
In each entire hair we perceive with the naked eye, an oblong slender filament, and a bulb at the extremity thicker and more transparent than the rest of the hair. The filament forms the body of the hair, and the bulb the root. The large hairs have their root, and even part of the filament, enclosed in a small membraneous vessel or capsule. The size of this sheath is proportionate to the size of the root, being always rather larger, that the root may not be too much confined, and that some space may remain between it and the capsule. The root or bulb has two parts, the one external, the other internal. The external is a pellicle composed of small laminæ; the internal is a glutinous fluid, in which some fibres are united; it is the marrow of the root. From the external part of the bulb proceed five, and sometimes, though rarely, six small white threads, very delicate and transparent, and often twice as long as the root. Besides these threads, small knots are seen rising in different places; they are viscous, and easily dissolved by heat. From the interior part of the bulb proceeds the body of the hair, composed of three parts; the external sheath, the interior tubes, and the marrow.
When the hair has arrived at the pore of the skin through which it is to pass, it is strongly enveloped by the pellicle of the root, which forms here a very small tube. The hair then pushes the cuticle before it, and makes of it an external sheath, which defends it at the time when it is still very soft. The rest of the covering of the hair, is a peculiar substance, and particularly transparent at the point. In a young hair this sheath is very soft, but in time becomes so hard and elastic, that it springs back with some noise when it is cut. It preserves the hair a long time. Immediately beneath the sheath are several small fibres, which extend themselves along the hair from the root to the extremity. These are united amongst themselves, and with the sheath that is common to them, by several elastic threads; and these bundles of fibres form together a tube filled with two substances; the one fluid, the other solid; and these constitute the marrow of the hair.