ART. I.-Recent Advances in the Etiology of Diseases of the Skin, and their Bearing upon Treatment. By WALTER G. SMITH, M.D., Physician to Sir Patrick Dun's Hospital; King's Professor of Materia Medica, School of Physic, Trin. Coll. Dubl.

In the present paper I propose to collect and summarise the results of some recent investigations. I shall endeavour to show the light which these doctrines and inquiries have thrown, and are calculated still more in the future to shed upon the group of diseases of the skin.

No attempt at a complete survey will be made, nor would, indeed, be possible in the time, and a restricted field-that of cutaneous diseases-is purposely chosen, for the sake of illustration, although it will be obvious that the facts to be referred to have a much wider scope.

For example, it will be remembered that last session in the Section of Pathology Dr. Bewley read an instructive paper upon the Pathology of Empyema, in which he showed that empyema is always due to the entrance of pus-producing organisms into the pleural cavity, either directly from without, or through a diseased lung, or by the route of the blood and lymph-vessels.

Results such as these have been acquired by the patient labours of experts in modern microscopical research. While only the *Read in the Section of Medicine of the Royal Academy of Medicine in Ireland Nov. 20th, 1891.

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minority can be fellow-workers in this attractive field, the rich harvest which is being garnered can and ought to be eagerly seized upon by all practitioners who desire to keep pace with the rapid strides of knowledge.

It is scarcely necessary to add that I do not at all wish to convey that dermatology is becoming a mere sub-section of bacteriology. Rather does the skin afford an epitome of general and special pathology, and the attempts to unravel its problems have been fruitful in elucidating pathological questions.

I shall allude more particularly to instances wherein our pathological conceptions have been simplified, and our views cleared, and hope to show that treatment has been rendered more rational and more successful.

If we glance at any of the current text-books upon Diseases of the Skin, we find a chapter or chapters devoted to the Vegetable Parasitic Diseases of the Skin. The affections usually described under this heading are some five or six in number.

Arranged in order of the discovery of their exciting cause, we start from the important discovery made in 1839 by Schönlein, who was the first to recognise and accurately describe the fungous character of the elements constituting a favus crust. To this succeeded the discovery by Gruby and Malmsten in 1843 of the fungus of ring-worm, and that of tinea versicolor by Eichstedt in 1846.

Notwithstanding the length of time these organisms have been known, and in spite of numerous investigations, their exact botanical affinities and mutual relationships have not yet been satisfactorily determined.

Even in the case of favus, whose clinical characters are so sharply defined, observers are not agreed as to whether we should acknowledge one only or several distinct forms of fungus."

Many other problems await solution, some of them of old standing-viz., whether alopecia areata is a parasitic disease or not. What a revolution is taking place in dermatology may be inferred from the fact that eleven years ago Kaposi, adverting to Hallier's mycological teaching, states that some of the investigations carried out in the direction indicated by him were so frivolous and resulted in such monstrosities that they excited the greatest mistrust of Hallier's results. "For," he scornfully adds, "there

• Cf. Pick und Král. Untersuchungen über den Favus. Monatsh. f. prakt. Dermat. XIII., p. 52.

was no single disease, whether warts, eczema, psoriasis, pruritus cutaneus, or inflammation, erysipelas, &c., which would not be attributed to a fungus" (Hebra, "Diseases of the Skin," New Sydenham Soc., Vol. V., p. 129).

Who, it may well be asked, would now deny that erysipelas and suppurative inflammations are due to parasitic organisms, to say nothing of the disputable ground presented by warts, eczema, and psoriasis.

When we consider the exposed position, the extent of surface, and the innumerable creases, folds, and crevices in the human epidermis, it is little matter for surprise that it has been found to be the home of a great variety of micro-organisms. Thus, Unna, in an investigation of sixty pure cultures from a series of cases of seborrhoeic eczema, discovered no less than fifty different Mucors, twenty different kinds of Penicillium, five Aspergilli, about a dozen forms belonging to the groups Oidium and Saccharomyces, besides a goodly number of partly known, partly unknown, cocci and bacilli. Král succeeded in growing three pure cultures of mould fungi from “eczema marginatum," all of which possessed the common property of flourishing luxuriantly at the body temperature, while at the temperature of the room they grew but slowly and imperfectly (Monatsh. f. prakt. Derm., 1890, p. 185).

In truth, there is an extensive Flora Dermatologica which vegetates upon the epidermis of man. The beginnings of our knowledge of it have been laid by Unna and his assistants, who have studied the appearances, macroscopic and microscopic, of these organisms, and their characters after cultivation in various media (Monatsh. f. prakt. Dermat., 1888, VII., p. 817, et seq.).

Many of these fungi are harmless, some are merely saprophytic, and a few are real mischief-makers (cf. Die Färbung der Mikroorganismen im Horngewebe. Unna. Monatsh. f. prakt. Derm. XIII., p. 325).

As a matter of convenience, I have distributed the illustrations which I shall adduce under separate propositions :

I. Some maladies hitherto ascribed to vague and unknown causes of internal origin are really traceable to infection, usually from without.

I shall upon this occasion dismiss with a nominal mention the case of lupus, whose specificity is generally acknowledged, and that of certain forms of purpura, which have been shown to be

* Cf. Kuhnemann. Monatshefte f. prakt. Dermatol. VIII., IX.

due to a fibrino-bacterial thrombosis (Tizzoni: Giovannini. de Guinard. Monatsh. f. prakt. Derm. X., p. 473; XI., p. 74).

Let us dwell shortly upon the examples of (a) erysipelas; (b) impetigo; (c) boils and carbuncles.

As to erysipelas, it may be regarded as proven that it is strictly caused by the intrusion of a streptococcus into the lymphatic channels of the skin or mucous membrane, and it is worth remarking that the contagious character of erysipelas was known in England long before it was recognised in Germany.

Erysipelas and lymphangitis are not convertible terms.

In connection with erysipelas, we are reminded of the interesting and important topic of the antagonism of micro-organisms, for erysipelas and vaccinia are examples of infective diseases, the artificial production of which has been suggested and used as a means of cure for other diseases-i.e., lupus, and certain forms of tumour (Fehleisen, Micro-parasites in Disease. Selected Essays, New Syd. Soc., p. 272; and Watson Cheyne, Lectures on Suppuration, p. 83).

Now, erysipelas often starts from a source of suppuration, and may itself be complicated by or end in suppuration, and, again, suppurative affections of the skin of primary and secondary origin are phenomena familiar to us in every-day practice.

It is generally held as settled that acute suppuration is, as Ogston first showed, due to the action of micro-organisms; but it is a difficult matter to determine whether erysipelas is an entity, a truly specific disease, or whether it does not represent a phase or mode of action of the pus-producing organisms. Watson Cheyne is inclined to uphold the specific character of the erysipelas germ, while Levy in a valuable paper (Archiv. f. exper. Path. u. Pharm. XXIX. Ueber die Mikro-organismen der Eiterung, p. 135), teaches that streptococcus pyogenes is at once an exciter of suppurative processes and of erysipelas. It is more than probable that there are several species of erysipelas due to different bacteria.

b

However this may be, it is a distinct advance in our knowledge to grasp the fact that the affections known as impetigo, boils, and carbuncles are invariably produced only under the influence of micro-organisms. We are thereby enabled to get clearer views of * Karlinski gives interesting statistics, based upon 200 cases of purulent inflammation, of the different forms of cocci and bacilli concerned (Monatsh. f. prakt. Derm. X., p. 420).

b Cf. Bockhardt's classical paper--Ueber die Ätiologie u. die Therapie der Impetigo, des Furunkels, u. der Sykosis-(Monatsh. f. prakt. Derm., 1887, p. 450).

their clinical history and progress, and our treatment is rendered less haphazard and more scientific.

The clinical differences in these affections can be explained by such considerations as these. Pus probably varies in virulence according to its origin, and pathogenic micro-organisms certainly vary in virulence according to the external conditions in which they find themselves. In a word, the character of the mischief doneLe., the type of the disease-depends not alone upon its direct cause, but also largely upon the mode of entrance and the seat of development of the organisms (Bockhardt: Garré).

Levy (loc. cit.) adduces evidence to show that the Bacterium coli commune may induce all possible forms of inflammation—viz., simple suppuration, inflammation of serous membranes, lymphangitis, and general blood-poisoning.

We are becoming more and more impressed with the conception, one of great importance, that the purely morphological study of bacteria is not the safe guide it was supposed to be in the dawn of bacteriology. A far more weighty point is the degree of virulence, coupled with investigations as to the conditions under which its virulence can be respectively augmented or attenuated.

We can easily see why pustular eruptions are common on the heads of children infected with pediculi. The reason is that pyogenic organisms often lurk beneath the nails or exist attached to hairs, and hence are readily inoculated by scratching into the little wounds inflicted by the pediculi.

It is an old observation, and one which Mr. Hutchinson has emphasised in his teaching (i.e., his aphoristic definition of Impetigo contagiosa-viz., "common, contagious, curable"), that pus is contagious; but, it should be remembered that pus, apart from the organisms which it contains, does not exert a pyogenic action (Cheyne). So that, strictly speaking, "impetigo contagiosa" does not represent a specific entity, because all forms of impetigo are, from their pathogenesis, contagious.

Considering the very great frequency of wounds and breaches of surface, it may appear strange that inflammatory and suppurative diseases are not more commonly met with. To this it may be replied that pyogenic organisms are not so abundant in the air as might be supposed, they are rarely present in putrefying fluids, and, moreover, they act only under certain special conditions. We are, besides, led by experience to conclude that susceptibility to the action of pyogenic organisms is, in many individuals, but slight.