We have now made sufficient progress in this enquiry to apply Bunsen's experiments in their relation to Dalton and Henry's hypothesis. If a given gas be absorbed at the same temperature, and by the same volume of a liquid, but under two different pressures, Po, P1, the amount of gas go, 91, absorbed in the two cases, respectively, is by equation (2)

These results show, within the limit of experimental error, the truth of the law for carbonic acid.

The ratio of absorbed gas to pressure is also shown very clearly in cases where partial pressures occur; that is, when the variation of pressure is effected by dilution with another gas. By means of formula (3), the composition of mixtures of two gases can be calculated when the constants of each gas are determined. If this calculated composition agree with that found directly by eudiometric analysis, it may be concluded that the law upon which the formula is based is true, and also that it is applicable for partial as well as for total pressures. The

following exhibits a mean of three experiments, taken at random from the numerous results obtained by Bunsen:—

An equally close agreement was found between absorptiometric and direct analysis in mixtures of carbonic acid and carbonic oxide. Mr. Watt says that the law also holds in mixtures of sulphurous acid with hydrogen and carbonic acid, and of carbonic oxide, marsh gas, and hydrogen; but not with a mixture of equal volumes of chlorine and hydrogen, or of chlorine with twice or four times its volume of carbonic acid ("Graham's Chemistry, Supplement," p. 651). Mr. Watt does not, however, cite his authority, and I have not met anywhere with an account of the experiments to which he refers. It may probably be assumed then, that the hypothesis of Dalton and Henry is true within ordinary limits, though it is also highly probable that in this law as in that of Mariotte, there exists a limit beyond which the regularity of the action is disturbed by the operation of varying molecular forces.

M. Bunsen gives an elaborate development of this law in its application to several problems of great interest and importance. A complete discussion of these would, however, exceed my limits, and I shall therefore merely notice those of more importance.

The quantitative composition of a gas, obtained by ordinary eudiometric analysis depends, almost entirely upon its supposed qualitative constitution. If, for example, a eudiometric experiment indicates the presence of marsh gas, it remains uncertain whether this is a mixture of equal volumes of hydrogen and methyle; or, if the presence of a mixture of marsh gas and hydrogen is indicated, it is quite uncertain whether that mixture consists of methyle and hydrogen, or of methyle, marsh gas, and hydrogen. Bunsen shows that in this and other similar cases all doubts are removed by absorptiometric experiments. When the absorption coefficients of gases are determined, three experiments are sufficient to determine the qualitative and quantitative composition of gaseous mixtures. There may be some cases, indeed, where the absorption curves of different gases approach, cut, or touch each other; and here a second experiment at a different temperature, or with another liquid, would be necessary. Hence, a determination of the amount of gases absorbed at various temperatures and by different liquids, becomes an important element in this species of analysis; for any number

of equations may thus be obtained, each of which possesses the value of an additional reagent.

In a similar manner, the alteration of constitution which a mixture of gases undergoes by contact with water may easily be determined by means of the absorptiometer. From the table of absorption coefficients given above, it will appear that inequalities of absorption of the component gases, may, under certain circumstances, induce very considerable error in eudiometric experiments, where gaseous mixtures are confined over water.

It is quite unnecessary that I should here enumerate the various ends which are subserved in nature by this property of absorption of gases. The absorption of air by the blood, of various gases by the juices of plants, and other applications, are sufficiently obvious. The purposes subserved by the inequalities of absorption for various gases and by different liquids, together with the effect of differences of temperature and pressure, are, however, still very imperfectly understood.

A remarkable illustration of the effect of inequality of absorption may be noticed in the phenomena of the oceanic atmosphere, which are, doubtless, to a considerable extent, dependent upon this cause. In the diminution of absorption, with increase of temperature also, we cannot fail to remark an endeavour of nature to increase the supply of nourishment to plants in cold climates, and to keep within limits, by a more sparing supply, the vegetation of the tropics.

The outline which I have now given of the present state of the enquiry into the "laws of the mutual interpenetration of fluids," shows that much remains for future research. The subject has, indeed, scarcely emerged from the field of natural history into that of physical science. Though it may not in itself appear so attractive as many other physical subjects, it is of especial interest and importance in its bearing upon the phenomena of osmosis, a subject on which I hope to make some remarks on a future occasion.

IV.-Cases of Induration of the Brain. By ALEXANDER ROBERTSON, M.D., Medical Officer, Town's Hospital, Glasgow.

ASSOCIATED with and evidently in a great degree resulting from that peculiar condition of the blood-that dyscrasis-which is induced by the abuse of alcoholic liquors, pathological anatomy reveals morbid conditions of most of the organs and tissues of the body. The liver may be found small, granular, and con

tracted, in a state of cirrhosis; or, it may be, a transformation of its tissue has taken place, fat globules have in a greater or less degree replaced the proper secreting structure and general parenchyma, giving rise to a form of the "fatty" liver; or, perhaps, the gland is simply in a state of hyperæmia, with the hepatic tubes distended with epithelial cells, secreted in excess from the abnormal stimulus. The kidney may be found in similar conditions--congested and enlarged, with the tubuli uriniferi packed with exfoliated cells and exuded fibrin; increased in bulk, yellow or mottled in colour, owing to the fatty degeneration of the proper gland substance of the organ, especially its epithelial cells; small, hard, and atrophied, the proper secreting tissue having broken down and been discharged, while the other tissues, subservient to it, are shrunk and contracted. The heart and great vessels may have become the seat of steatosis with resulting cardiac hypertrophy and dilatation. The muscular system, voluntary or involuntary, may also have suffered from fatty degeneration; and even the osseous tissue may be similarly affected. The nervous system is involved in the general morbid change. Its tissue is hardened and atrophied, and sometimes the seat of an albuminoid development. The blood itself is deficient in fibrin, and often abounds in fat globules. But we seldom, even in confirmed drunkards, find all the organs in one or other of the conditions described; and, if so, the majority are only implicated in a minor degree. More frequently one, or at most two of the principal organs, exhibit marked evidence of diseased action. The liver probably suffers most frequently. The kidneys are also very often involved. The brain is seldom affected to so serious a degree as to induce a fatal result from a direct interference with its functions. These are more generally impaired or destroyed from the impure blood which circulates in the cerebral vessels, owing to the non-elimination of those effete products of the tissues which form the special secretions of the kidney and liver, according as either or both of these organs are implicated. In the cases which I am now about to record, the brain was the organ most seriously suffering, and the unfavourable termination was especially due to the cessation of its functions :

Case I.-M. C., aged 19, millworker, admitted September 14th, 1860.

History and State on Admission.-For three years has led a very irregular life, and has been in the habit of drinking, especially whisky, to great excess. Has not menstruated for two and a half years. Two months ago began to suffer from marked debility, gradually increasing, and accompanied by cough and slight irregular pain in chest. About a month since eyesight

began to fail, and is steadily getting worse. Now, can with difficulty distinguish objects, unless they are prominent and close to her. Is stupid and confused, but answers relevantly simple questions, although usually only after they are repeated. Staggers when walking, evidently from a loss of muscular power. Arms are also slightly paralyzed. In speaking, pronounces the words slowly, but more from stupidity than inability to articulate. Sensation appears dulled, but to what degree cannot be ascertained from the impairment of her mental powers. Making allowance for the last condition, hearing seems tolerably acute. Pupils are widely dilated, and respond slowly and imperfectly to the stimulus of light. Conjunctivæ are clear and not at all injected. Urine and stools are frequently passed in bed, but the sphincters are evidently not involved to a great extent, as she is occasionally cleanly in her habits. The urine is quite normal in character. Percussion and auscultation reveal nothing abnormal in chest, except a few mucous râles. Hepatic and splenic dulness are also natural. Pulse 84, full. General condition spare and anæmic. No evidence of syphilis. Her symptoms gradually grew more unfavourable. Amaurosis became complete. Paralysis was more developed. Stupor increased, and eventually subsided in coma, which speedily terminated fatally-death occurring a month after admission.

The treatment consisted chiefly in counter-irritation by blisters to the entire head, and, at first, purgation.

Post-mortem.-Calvarium and dura mater normal. Arachnoid slightly opaque, particularly in the course of the superior longitudinal sinus. Glandulæ Pacchioni unusually large. Pia mater injected, but not intensely so. A slight increase of fluid in cavity of arachnoid. A hard body, about the size of a small bean, gritty to the touch, and apparently of a calcareous nature, was found in left choroid plexus. The white substance was pale, and the brain generally less vascular than usual. The most marked morbid change was the uniform increase in density and toughness, so much so, that it required considerable force to pass the finger into either the grey or white substance. In fact, it resembled very much a brain that had been steeped for a few days in alcohol, only that there was little, if any, appreciable contraction.

Remarks. In this girl of 19 there existed an induration of the brain, which is rarely found except in aged drunkards; but it differed in this respect, that it was unaccompanied by any decided atrophy. Possibly this apparent absence of atrophy may have resulted from an albuminoid development, compensating for the contraction of the normal tissue, and resulting from a degree of vascular overaction in the course of her disease. Such a development is believed to take place in hypertrophy of