inflammation, which leads inevitably to ulceration of the cornea, conjunctiva, etc., unless the eye be shielded from external irritants. Section of both pneumogastric nerves is likewise followed by a condition of inflammability in the lung, whence develops rapidly a pneumonia, due to the irritation of the liquids of the mouth, which are unhindered from flowing into the bronchi.

Convulsions and hyperesthesia may at times also lead to trophical disturbances, but this is in rare cases, where they appear as persistent affections.

The more "independent tropho-neuroses " include any number of atrophies, inflammations, and gangrenous processes. Their whole aspect intimates the participation of the nervous system, although it cannot as yet be satisfactorily proved that they originate in any definite local alterations of the same. Among simple atrophies we may specify those which attack one-half of the face and extremities; those causing sudden whitening of the hair, from fright and anxiety; those causing loss of hair in patches in what is called the area Celsi, and the scattered white patches in chorea minor.

The most perplexing of all are certain inflammations of the skin which coincide to all appearances with affections of sensitive nerves, particularly herpes zoster. Violent itching accompanies the appearance upon the skin, over the course of certain sensitive nerves, of a group of pearl-sized vesicles. Their arrangement marks very distinctly the course of the nerve-for example, that of an intercostal nerve. After a few days they dry up and heal over. Von Bärensprung and von Recklinghausen have discovered in this disease an inflammatory redness of the corresponding intercostal nerves and of the intervertebral ganglion, and this very nearly establishes the participation of the sensitive nerves in the formation of these vesicles. "Psoriasis cutanea," which is marked by the presence of numerous red and slightly swollen patches and abundant epidermic products, also hints at a nervous origin, by the symmetry of the exanthema which often breaks out on the back. It may pass for a statement subject to many limitations, when I ascribe these neurogenous inflammations to the confluence of two etiological influences, each of which would of itself be insufficient to achieve the same result. These are (1) an angio-neurosis, or, at least, a tendency towards vascular dilatation, due to the local derangement of certain

sensitive centres; (2) an accumulation, as in the case of trigeminal ophthalmia, of the usually ineffectual irritants of the skin, which, on account of a local affection, cannot be discharged, and hence produce a much more powerful local effect.

To the latter agency we may refer all cases of "neurotic gangrene," whose whole expression and diffusion are suggestive of decubitus paralyticus, water cancer (c. aquaticus, Noma), mal perforant du pied, symmetrical gangrene of the face, and leprous necrosis, where the insufficient centripetal removal of peripheral irritation is especially conspicuous in the anæsthesia produced by leprous neuritis, which accompanies it.

IV. SPECIAL PART.

The species morbi is determined by the cause of disease, on which depends the point of attack-and I might almost say-the entire plan of attack of a disease. The cause of disease regulates the order and the manner in which the organs shall be attacked; whether, and at what time fever shall set in, as well as the intensity and particular type of the same; and the degree of injury to the heart and sensorium. The cause of disease, in short, includes everything by which we distinguish one disease from another. There is no other distinction but that of cause, which furnishes those peculiarities of diseases, by which they can be readily classified into major and minor varieties.

It is, of course, understood that such a classification is only concerned with the actual and genuine causes of disease, excluding all that is casual and irregular. We can conceive of an etiological division of diseases which would be governed by the vehicle through which the disease is conveyed to us. In such a case we would have nutritive diseases, infectious diseases, climatic diseases, diseases due to certain vocations, etc. This system, although etiological, is purely artificial, and could not, for a moment, be seriously entertained. The following pages are devoted almost exclusively to the question of food, clothing, atmosphere and infection. Natural groups of diseases are only formed when we adopt as the standard of division the independent agency of the cause of disease as well as its quality and natural history existence.

Thus we have five chief classes, to which there is at present added a sixth, Idiopathic, i. e., diseased conditions whose causes are as yet unknown.

(1) Traumatic diseases; (2) Parasitic disease; (3) Diseases due to defective nutrition and growth; (4) Diseases of over-exertion; (5) Diseases of premature senility.

It not unfrequently happens that several distinct diseases occur in one individual. In such cases clinical analysis is not content merely to notice the various concurrent etiological

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phenomena, but it makes them of first importance in diagnosis, prognosis and therapeutics. Thus it is evident that medical instinct has long since accustomed itself to perceive in any given illness a plurality of diseases. Such a patient represents to us, not, as he imagines, one disease, but several diseases, whose symptoms either co-exist independently, or interfere with each other, and furnish products of amalgamation.

I. TRAUMATIC DISEASES.

Trauma, in its broadest sense, is any external attack which forcibly alters the physical or chemical composition of a part or the whole of the body. Hence we distinguish mechanical, chemical, electrical traumata, and traumata due to the extremes of heat or cold.

(a) MECHANICAL TRAUMA.

In order to comprehend the attitude of the body towards the various mechanical assaults to which it is exposed, we must first of all concede that, in structure and texture, it is so ingeniously contrived as to offer the greatest possible resistance to mechanical agencies. The brittle and sensitive bones are generally enveloped in a thick sheath of soft elastic substances, and the skin is of such decided elasticity and firmness that it resists the pressure of a blunt surface by an incredible amount of stretching, even allowing brief but extensive displacements of the subcutaneous parts without itself becoming lacerated. But everything has its limit, and there are a series of mechanical traumata which effect a permanent breach of continuity; such are incisions, bites and lacerations, blows, knocks, stings, contusions and falls.

"Solution of continuity" is the first and general result of every mechanical trauma. This is usually well marked when the parts are really cut with a sharp instrument, or in a genuine fracture of the bones. There are bruises and contusions which produce solutions in continuity in the more delicate structural parts, where the pathological condition is not at all perceptible immediately after the injury. In such instances the depth of the lesion inflicted can only be judged by the irrevocable loss of function (commotio cerebri) or by the gangrene which at once sets in (subcutaneous contusions, as in kicks from a horse). Apart from these, we must consider, in a fresh wound: the amount of blood lost or still

escaping; the possibility of air or fat entering the blood paths; the loss or destruction of tissue; the entrance of foreign substances into the wound; and, finally, the quality of the injured parts, which determines on the one hand the value of the functional disturbance, on the other the local probabilities of

recovery.

The reunion of the divided parts, their restitution as a scar, the closing up of the bodily parenchyma exposed by the wound-in short, the healing of the lesion-is not so much the deliberate intention of the recuperative powers of nature as it is the result of an inflammatory process, which has been induced by the mechanical irritation of the parts. A hyperæmia of the remaining intact blood vessels leads to a serocellular exudation, which is directed from all quarters towards the injured spot. Here the exudate reaches those portions of the tissues whose nutrition has been threatened by the traumatic lesions which they have suffered. In favorable cases, we have to do with but a thin tissue stratum, which, when the parts are properly and promptly approximated, can be nourished by the aid of the exudate, until a sufficient number of new formed vessels, together with a moderate supply of connective tissue, reunite the edges of the wound (union by first intention). In less favorable cases, both large and small shreds of tissue undergo necrosis, and must, together with all other foreign matters, be loosened and removed before the edges can reunite. The cleansing and healing up of the wound by second intention is accomplished by granulation tissue, which establishes a layer of pus at the junction of the healthy and necrosed parts, separating the two, but soon leading to cicatrization. The epithelial covering of the surface is derived from the surrounding epithelial borders.

Disturbances in these processes are mainly due to the deposition in the wound of a cleft fungus, Billroth's cocco-bacteria septica. Since we have learned from Lister how to frustrate the poisonous influence of this fungus, exerted upon the blood and juices of the body, wounds complicated with septicemia, pyæmia, diphtheria, and erysipelas are exceptional; in residences and towns they no longer occur epidemically. A more careful discussion of this subject will be found under the head of infectious diseases.

Thrombosis and embolism are favorite elements of pyæmia, to which they impart a metastatic character. They appear,