"blood disease," "good blood," "bad blood," "pure blood," “impure blood," "poisoned blood: " these and many other similar terms convey the idea that the blood is a very centre of all the diseases of mankind.

But when we come to precise facts, when we condescend to learn the true and fixed local diseases concentrated in the blood, great difficulties at once appear; because, after all, the blood, a constantly regenerated fluid, is but the channel through which diseased conditions, lying apart from itself, are temporarily presented. The blood may be the means of conducting or conveying into the tissues agents which may be poisonous, and so it may be itself poisoned from without. The blood may be the means, and is the means, of conveying poisonous products out of the body and of presenting them for oxidation and destruction to air, and so it may be poisoned from within. Both, however, of these states are but passing phases, and the same holds good in respect to all other conditions of disease, with a few exceptions to the contrary so rare they may be allowed to pass without special notice. The blood, in brief, is the whole body in transitory solution, and is the representation of the body in that state.

It is difficult, consequently, to name any permanent local diseases of the blood; but it is not without service to look at some changes in its constituent parts, which may be called its local temporary disorders or diseases.

Increase of Water of Blood.

The blood contains naturally 790 parts per 1,000 of water, and its specific gravity is 1.055. In some forms of disease, such as dropsy, the quantity of water may be largely increased. The blood of a woman who was suffering from ovarian dropsy, I found to have a specific gravity of not more than 1.016. Such blood is incapable of sustaining the natural functions of life.

Decrease of Water of Blood.

In certain exhausting diseases, such as cholera, where mere is a constant drain of watery fluid from the body, the blood may be left so dense from loss of its water that it may cease to be able to flow through the minute vessels.

Increase of Fibrine in the Blood.--Hyperinosis.

The blood naturally contains from two to three parts in the thousand of the plastic coagulable colloid called fibrine, which while circulating in the vessels is in the fluid state, but which, when the blood flows out of the body, sets or clots. In some conditions of the body the fibrine undergoes increase in the blood, especially in various forms of local inflammations, such as pneumonia, or inflammation of the lungs, croup, and malarial fever. In extreme instances it may increase to the extent of nine parts in the thousand. When an increase of the fibrine of the blood is present the tendency is to its deposition and to the formation of those fibrinous concretions which the ancient physicians called polypi, and which we have seen classified amongst the local diseases of the heart and blood-vessels.

Decrease of Fibrine in the Blood.-Hypinosis.

In some conditions the fibrine is decreased to one or even a lesser part in the thousand parts of blood. Blood so circumstanced is often uncoagulable; it easily flows out of the vessels, and if a small wound be made, a wound from the bite of a leech, for example, the bleeding may continue to a fatal issue. This state of fluid blood may give rise to an eruption on the body of dark spots like bruises, and to one form of the disease known as purpura. Children are sometimes born with the blood in this state of extreme fluidity, and in exceptional instances the affection is hereditary.

Decrease of Red Corpuscles of Blood.

The natural blood contains one hundred and twenty-seven parts in the thousand of corpuscular matter, made up in great part of the little circular red disks containing a substance known as hæmaglobin, in a thousand parts of which there is four and one-fifth of the metal iron. The corpuscles may be greatly reduced in amount without actual danger to life; but the reduction of them gives rise to paleness of the blood, and, as they are the bearers of the oxygen of the external air into the body, such reduction gives rise also to paleness and feebleness of the body, and to defective nutrition. The disease "anæmia" is due to a reduction of red corpuscles in the blood, and the "anæmic state,"

from the same cause, is present in many lingering and wasting diseases. The term "poor blood" is commonly used to indicate this state.

Injury and Destruction of Red Blood Corpuscles.

The red corpuscles of the blood are subject to injury, and even to destruction, by various agents acting on the body. By admixture of ammonia and of other alkalies with the circulating blood the corpuscles can be wholly or partly dissolved, made crenate at their margins, and irregular as if indented or notched. By the smoke of tobacco they are modified in a similar form. By alcohol taken freely into the body they are reduced in size, and lose their true rounded form, becoming long and "truncated." In blood surcharged with soluble saline substances they are reduced in size, shrunken. In blood surcharged with water they are increased in size, lose their flattened form and depressed centres, and become of rounded or globular shape. In instances in which the blood is surcharged with carbonic acid, the corpuscles lose their red color, and the mass of the arterial as well as of the venous blood becomes dark in color.

Under all these varying states, the natural function of the blood corpuscle, its power to condense the oxygen of the air which it meets as it circulates through the lungs, and to convey oxygen into the ultimate tissues of the body for supporting the combustion and the nutritive changes, is perverted. Thereupon the healthy state of the body is rendered impossible, and various inodifications of organic functions are set up, which, if long continued, lead, of necessity, to natural perversion of function and proclivity to disease.

Increase of the White Corpuscles of Blood. Leucocythæmia.

Besides the red corpuscles there are, as we know, in the natural blood a number of other corpuscles, far less numerous than the red, which corpuscles are colorless, called therefore the white or colorless corpuscles of the blood. In some forms of disease, especially from changes in certain organs of the body, as the spleen, the white corpuscles increase, and the blood becomes surcharged with them, the red corpuscles being at the same time. relatively decreased. The disease so produced is called "white blood cell disease," or leucocythæmia, a disease of serious import.

It is accompanied with paleness of the body, great languor and depression, and impaired nutrition. White blood cell disease is probably hereditary in character, and up to this time has been little amenable to treatment. It was discovered in 1845 by the late Dr. Hughes Bennett of Edinburgh, one of the few illustrious in medicine of this age.

Poisoned Conditions of Blood.

The blood, lastly, may be charged with poisonous substances which so interfere with its function that death may be the result. These poisons may be derived from without, as when a gaseous or vaporous body, such as nitric acid vapor, or chlorine gas, or ammonia vapor is inhaled; or they may be derived from rapid changes excited in the body itself by some animal poisons, such as snake poison, with which the body has been inoculated; or they may be derived from substances which are natural to the body formed in excess, such as urea, the natural soluble salt of the urine. In yellow fever ammonia has been formed in such excess in the body as to reduce the blood to a fluid like port wine in consistency, the corpuscles being dissolved altogether, and their coloring matter being diffused through the whole mass of the blood like a dissolved coloring principle or dye.

CHAPTER IV.

LOCAL DISEASES OF THE BREATHING OR RESPIRATORY

SYSTEM.

UNDER the respiratory system is included all the organs and parts concerned in the act of respiration or breathing; the nostrils, larynx, and glottis; the trachea or windpipe; the bronchial tubes; the structure of the lung proper, including the air-vesicles; the pulmonic vascular plexuses; the nervous filaments; the elastic connective tissue; the covering of the lung or pleural membrane; and the space between the lung formed by the meeting of the pleura of each lung-the mediastinum. The diseases of this system represent a numerous class.

NASAL CATARRH. CORYZA.

Nasal catarrh is a discharge of fluid from the nose, called also common cold. It is a well-known affection, becoming often epidemic, lasting usually from three to five days, and, when severe, attended with pain and sense of weight in the head, pain in the limbs, great depression of the physical powers, and irritability and inactivity of mind. There is usually a few degrees of fever during the presence of catarrh.

CROUP.

A diseased condition of the larynx and trachea, in which the breath is drawn through those parts with difficulty, and with the production of a hard or croupy sound, which may become so intense as to be actually ringing and shrill. There are two distinct varieties of croup, the spasmodic and membranous.

A

Spasmodic croup.-Called sometimes Laryngismus Stridulus. spasm of the glottis or opening through the larynx into the windpipe and lungs attended with croupy breathing. The dis