tinuous. If mercury as a liquid is opaque and as a gas is transparent, the red and translucent bromine, on the other hand, when heated above the critical point, becomes so opaque as almost to resemble a mass of resin. Frankland has shown that the flame of hydrogen becomes continuous when the gas is burned under a pressure of 20 atmospheres, and these experiments have been since extended by the same able chemist and Lockyer. We must not, however, suppose that one intermediate state exists between liquid and gas; on the contrary, an infinite succession of intermediate states may truly be said to connect the liquid proper and the gas proper; in other words, the passage is continuous. When the critical point is attained, the density of the liquid and gas becomes the same, and the tube is filled with homogeneous matter. As regards the question of the continuity of the solid and liquid states, it would be necessary, in order to establish this continuity, to obtain, by the combined action of heat and pressure, the solid and liquid of the same density and of like physical properties. To accomplish this result will probably require pressures far beyond any which can be reached in transparent tubes; but it may be possible to show by experiment that the solid and liquid can be made to approach to the required conditions. [T. A.] GENERAL MONTHLY MEETING, Monday, June 5, 1871. SIR HENRY HOLLAND, Bart. M.D. D.C.L. F.R.S. President, Silas Kemball Cook, Esq. Miss Elinor Martin, Charles Bland Radcliffe, M.D. were elected Members of the Royal Institution. The special thanks of the Members were returned for the following Donation to "The Fund for the Promotion of Experimental Researches":— Sir Henry Holland, Bart. (13th Annual Donation) .. £40 The PRESENTS received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. : FROM Asiatic Society of Bengal-Journal, No. 160. 8vo. 1871. Astronomical Society, Royal-Proceedings, Vol. XXXI. No. 6. 1871. British Architects, Royal Institute of-Sessional Papers, 1870-71. No. 9. 4to. Chemical Society-Journal for May, 1871. 8vo. Editors-Academy for May, 1871. 4to. American Journal of Science, April, 1871. 8vo. Artizan for May, 1871. 4to. Athenæum for May, 1871. 4to. Chemical News for May, 1871. 4to. Engineer for May, 1871. fol. Food Journal for May, 1871. 8vo. Horological Journal for May, 1871. 8vo. Pharmaceutical Journal for May, 1871. 8vo. Franklin Institute-Journal, Nos. 542, 543. 8vo. 1871. Medical and Chirurgical Society, Royal-Proceedings, Part 32. 8vo. 1871. Preussische Akademie der Wissenschaften-Monatsberichte, April, 1871. 8vo. Royal Society of Tasmania-Proceedings, 1868, 1869. 8vo. 1869-70. Vereins zur Beförderung des Gewerbfleisses in Preussen-Verhandlungen, Jan.Feb. 1871. Wilkinson, F. C. Esq.-The Gospel according to St. Mark (translated by J. Ivatt Briscoe). 4to. 1870. Zoological Society of London-Transactions, Vol. VII. Parts 3, 4, 5. 4to. 1871. Proceedings for 1870. 8vo. 1871. WEEKLY EVENING MEETING, Friday, June 9, 1871. SIR HENRY HOLLAND, Bart. M.D. D.C.L. F.R.S. President, JOHN TYNDALL, Esq. LL.D. F.R.S. PROFESSOR OF NATURAL PHILOSOPHY, ROYAL INSTITUTION, On Dust and Smoke. AFTER a few preliminary experiments illustrative of the polarization of light, Professor Tyndall adverted to the polarization of light by fine dust, by the sky, and by the coarser particles of smoke. In the former the direction of maximum polarization, as in the case of the sky, is at right angles to the illuminating beam. In the latter, according to the observations of Govi, the maximum quantity of polarized light was discharged obliquely to the beam. Govi's observation of a neutral point in such beam, on one side of which the polarization was positive and on the other side negative, was also referred to. The additional fact was then adduced that the position of the neutral point varied with the density of the smoke. Beginning, for example, with an atmosphere thickened by the dense fumes of incense, resin, or gunpowder, and observing the neutral point, its direction was first observed to be inclined to the beam towards the source of illumination. Opening the windows so as to allow the smoke to escape gradually, the neutral point moved down the beam, passed the end of a normal drawn to the beam from the eye, and gradually moved forward several feet down the beam. The speaker did not halt at these observations; they were introduced as the startingpoint of inquiries of a different nature, and after their introduction the discourse proceeded thus: But what, you may ask, is the practical good of these curiosities? And if you so ask, my object is in some senses gained, for I intended to provoke this question. I confess that if we exclude the interest attached to the observation of new facts, and the enchancement of that interest through the knowledge that by-and-by the facts will become the exponents of laws, these curiosities are in themselves worth nothing. They will not enable us to add to our stock of food, or drink, or clothes, or jewellery. But though thus shorn of all usefulness in themselves, they may, by leading the mind into places which it would not otherwise have entered, become the antecedents of practical consequences. In looking, for example, at this illuminated dust, we may ask ourselves what it is. How does it act, not upon a beam of light, but upon our own lungs and stomachs ? The question at once assumes a practical character. We find on examination that this dust is organic matter-in part living, in part dead. There are among it particles of ground straw, torn rags, smoke, the pollen of flowers, the spores of fungi, and the germs of other things. But what have they to do with the animal economy? Let me give you an illustration to which my attention has been lately drawn by Mr. George Henry Lewes, who writes to me thus : "I wish to direct your attention to the experiments of Von Recklingshausen should you happen not to know them. They are striking confirmations of what you say of dust and disease. Last spring, when I was at his laboratory in Würzburg, I examined with him blood that had been three weeks, a month, and five weeks, out of the body, preserved in little porcelain cups under glass shades. This blood was living and growing. Not only were the Amoeba-like movements of the white corpuscles present, but there were abundant evidences of the growth and development of the corpuscles. I also saw a frog's heart still pulsating which had been removed from the body (I forget how many days, but certainly more than a week). There were other examples of the same persistent vitality or absence of putrefaction. Von Recklingshausen did not attribute this to the absence of germs-germs were not mentioned by him; but when I asked him how he represented the thing to himself, he said the whole mystery of his operation consisted in keeping the blood free from dirt. The instruments employed were raised to a red heat just before use, the thread was silver thread and was similarly treated, and the porcelain cups, though not kept free from air, were kept free from currents. He said he often had failures, and these he attributed to particles of dust having escaped his precautions." Professor Lister, who has founded upon the removal or destruction of this" dirt" great and numerous improvements in surgery, tells us the effect of its introduction into the blood of wounds. He informs us what would happen with the extracted blood should the dust get at it. The blood would putrefy and become fetid; and when you examine more closely what putrefaction means, you find the putrefying substance swarming with organic life, the germs of which have been derived from the air. Another note which I received a day or two ago has a bearing particularly significant at the present time upon this question of dust and dirt, and the wisdom of avoiding them. The note is from Mr. Ellis, of Sloane Street, to whom I owe a debt of gratitude for advice given to me when sorely wounded in the Alps. "I do not know," writes Mr. Ellis, "whether you happened to see the letters, of which I enclose you a reprint, when they appeared in 'The Times.' But I want to tell you this in reference to my method of vaccination as here described; because it has, as I think, a relation to the subject of the intake of organic particles from without into the body. Vaccination in the common way is done by scraping off the epidermis, and thrusting into the punctures made by the lancet the vaccine virus. By the method I use (and have used for more than twenty years) the epidermis is lifted by the effusion of serum from below, a result of the irritant cantharadine applied to the skin. The little bleb thus formed is pricked, a drop of fluid let out, and then a fine vaccine point is put into this spot, and after a minute of delay it is withdrawn. The epidermis falls back on the skin, and quite excludes the air-and not the air only, but what the air contains. "Now mark the result-out of hundreds of cases of re-vaccination which I have performed, I have never had a single case of bloodpoisoning or of abscess. By the ordinary way the occurrence of secondary abscess is by no means uncommon, and that of pyæmia is occasionally observed. I attribute the comparative safety of my method entirely, first, to the exclusion of the air and what it contains; and, secondly, to the greater size of the apertures for the inlet of mischief made by the lancet." I bring these facts forward that they may be sifted and challenged if they be not correct. If they are correct it is needless to dwell upon their importance, nor is it necessary to say that if Mr. Ellis had resigned himself wholly to the guidance of the germ theory he could not have acted more in accordance with the requirements of that theory than he has actually done. It is what the air contains that does the mischief in vaccination. Mr. Ellis's results fall in with the general theory of putrefaction propounded by Schwann, and developed in this country with such striking success by Professor Lister. They point, if true, to a cause distinct from bad lymph for the failures and occasional mischief incidental to vaccination; and if followed up they may be the means of leaving the irrational opposition to vaccination no ground to stand upon, by removing even the isolated cases of injury on which the opponents of the practice rely. We are now assuredly in the midst of practical matters. With your permission I will recur once more to a question which has recently occupied a good deal of public attention. You know that as regards the lowest forms of life, the world is divided, and has for a long time been divided, into two parties, the one affirming that you have only to submit absolutely dead matter to certain physical conditions to evolve from it living things; the other, without wishing to set bounds to the power of matter, affirming that in our day no life has ever been found to arise independently of pre-existing life. Many of you are aware that I belong to the party which claims life as a derivative of life. The question has two factors: the evidence, and the mind that judges of the evidence; and you will not forget that it may be purely a mental set or bias on my part that causes me throughout this discussion from beginning to end, to see on the one side dubious facts and defective logic, and on the other side firm reasoning and a knowledge of what rigid experimental inquiry demands. But judged of practically, what, again, has the question of Spontaneous Generation to do with us? Let us see. There are numerous diseases of men and animals that are demonstrably the products of parasitic life, and such diseases may take the most terrible epidemic forms, as in the case of the silkworms of France in our day. Now it is in the highest degree important to know whether the parasites in question are spontaneously developed, or are wafted from without to those afflicted with the disease. The means of prevention, if not of cure, would be widely different in the two cases. But this is by no means all. Besides these universally admitted cases, there is the broad theory now broached and daily growing in strength and clearness-daily, indeed, gaining more and more of assent from the most successful workers and profound thinkers of the medical profession itself the theory, namely, that contagious disease generally is of this parasitic character. If I had heard or read anything since to cause me to regret having introduced this theory to your notice more than a year ago, I should here frankly express that regret. I would renounce in your presence whatever leaning towards the germ theory my words might then have betrayed. Let me state in two sentences the grounds on which the supporters of the theory rely. From their respective viruses you may plant typhoid fever, scarlatina, or small-pox. What is the crop that arises from this husbandry? As surely as a thistle rises from a thistle seed, as surely as the fig comes from the fig, the grape from the grape, the thorn from the thorn, so surely does the typhoid virus increase and multiply into typhoid fever, the scarlatina virus into scarlatina, the small-pox |