2.^,0 



NATURE 



{Jan. 18,1872 



the success of the experiment with the elastic band de- 

 pends upon the band being of a certain thickness, and 

 upon the weights being so adjusted as to balance without 

 overbalancing its elasticity. Failing these conditions 

 charge anddischarge may nottell in causingelongation and 

 contraction. And, therefore, the absence of perceptible 

 elongation and contraction in the nerve-fibre under the 

 charge and discharge may be simply owing to the fact 

 that the thickness and stretching of the neurilemma have 

 not been adjusted for the production of these results. 

 Besides, it is by no means certain that there are not in 

 some nerve-fibres slight changes which are strictly parallel 

 to the elongation and contraction witnessed in muscular 

 fibres. 



In a word, there seems to be good reason for believing 

 that in nerve as in muscle electricity may have to do 

 much of what is commonly regarded as the special work 

 of an inherent vital principle. 



4. How in inaintainiug the " tone of the system " elec- 

 tricity may liave to do much of what is commonly re- 

 garded as the special work of a 7'ital principle. 



After what has been said little remains to be added un- 

 der this head. The conclusion arrived at is that each 

 perfect fibre and cell of living muscle and nerve (and, by 

 implication, every living fibre and cell), is a charged 

 leyden-jar while at rest. It is that the membranous 

 portion of the fibre or cell is at this time compressed 

 by the mutual attraction of the two opposite charges 

 disposed leyden-jar- wise upon its two surfaces. It is 

 that the effect of this compression is to elongate the fibre 

 or cell by squeezing out this membrane lengthwise. What 

 then ? May it be that this compression, this squeezing 

 out, is sufficient to account for what is called the " tone of 

 the system" ? This state, no doubt, is indefinite enough, 

 but it becomes more definite when viewed in this way — 

 so definite, in fact, that here also, in the maintenance of 

 the '■ tone of the system " that is to say, electricity may 

 have to do much of what is commonly believed to be the 

 work of a vital principle. 



5. How in certain processes of growth electricity may 

 do much, of what is commonly regarded as the special 

 work of a vital principle. 



A cell or fibre is at first a mass of protoplasm without 

 any investing membrane. Later, this membrane makes 

 its appearance, and how is this ? Is it that the surface of 

 the protoplasmic mass, except at the part or parts where 

 the nucleus is afterwards met with, hardens by desiccat- 

 ing, or dying, or changing in some other way, and, so 

 hardening, acquires dielectric properties ? Is it that 

 the molecular changes ever going on in the protoplasmic 

 matter beneath this crust, develope a charge on the inside 

 of this crust, which, acting inductively, leads to the de- 

 velopment of the opposite charge on the outside ? Is it 

 that the compression arising from the mutual attraction 

 of these opposite charges, causes the crust to stretch out 

 every way, and so separate from the underlying proto- 

 plasmic mass, leaving thereby in some instances a vacuole, 

 which may be filled with a thin liquid or even air.' Is 

 this the way in which the sarcolemma and neurilemma, 

 the cell-walls, and all membranes more or less analogous 

 to them, may be formed } After what has been said such 

 an idea is by no means improbable. Nay, such an idea 

 may be looked upon as the natural consequence of the 

 premises. And if so, then electricity may have to do 

 much of what is commonly believed to be the work of a 

 vital principle in these phenomena of growth, as well as 

 in the various processes which have been already passed 

 in review, and upon which so much has been said as to 

 leave only room now for these bare hints of what might be 

 said upnn the subject. 



C. B Rapli.iffe 



MERCURY PHOTOGRAPHS 



AN entirely novel method of photographic printing has 

 just been discovered by M. Merget of Lyons. 

 Although akin in some respects to the daguerreotype pro- 

 cess, it differs essentially therefrom in the fa;t that expo- 

 sure to light is not necessary to the formation of every 

 separate image. It is difficult indeed just now to apply 

 any distinguishing name to M. Merget's invention, for the 

 methods hitherto discovered — and the number of these 

 has, we all know, increased of late beyond all calculation 

 — are all of them divisible into two very distinct classes. 

 Thus we have those processes broadly termed chemical, 

 in which every print is secured by the aid of light, as for 

 instance, the nitrate of silver and carbon methods ; and 

 those again where a matrix, or printing block, having 

 been prepared, the copies are struck off in the ordinary 

 lithographic or printing press ; photographs prepared in 

 this latter manner are usually termed photo mechanical 

 prints. M. Merget's invention partakes singularly enough 

 of the nature of both classes ; for while the prints are un- 

 doubtedly formed by chemical action, the question of 

 light is of no moment at all, and the manipulations in- 

 volved are to some extent of a mechanical nature. 



The experiments of Faraday upon the diffusion of 

 gases will be remembered by many, and it was the re- 

 sults arrived at by that distinguished philosopher that 

 incited M. Merget, the Professor of Physics at the Faculte 

 des Sciences of Lyons, to take up the investigation he 

 has so successfully carried through. Faraday had already 

 found out that the vapour of mercury acted very sensibly 

 upon gold-leaf, and the first task undertaken by M. Mer- 

 get was to discover whether this same action also took 

 place upon other metals or their compounds. The in- 

 vestigation, it should be stated, was designed to be of a 

 purely theoretical nature, and was not undertaken, in the 

 first instance at any rate, with a view of working out any 

 practical processes such as may eventually result from 

 the research. The principal points discovered by M. 

 Merget may be thus summarised ; — 



1. The vaporisation of mercury is a continuous pheno- 

 menon ; that is to say, the metal emits vapour at all times, 

 even at a very low temperature, and when in a solidified 

 form. 



2. Mercury vapour may be condensed upon certain 

 substances, such as carbon, platinum, &c., without these 

 latter being chemically affected. 



3. Mercury vapour will pass with exceeding facility 

 through porous bodies, such as wood, porcelain, &c. 



4. The salts of all precious metals when in solution are 

 very sensitive to the action of mercury vapour, which has 

 the effect of rapidly reducing them. 



The most sensitive to mercury of the precious metal 

 salts are nitrate of silver and the soluble chlorides of 

 gold, palladium, and iridium, and paper prepared with 

 any of these forms at once a most delicate test for the 

 volatile metal ; but the solutions must contain some 

 hygrometric body to prevent complete desiccation, so that 

 the surface coated with them will always remain in a moist 

 condition. To demonstrate how exceedingly sensitive this 

 test-paper is to mercury, we may state that its contact with 

 anybody containing but a slight trace of amalgam suffices 

 to darken the surface, while it is affirmed that any workman 

 who has been employed for some time in a looking-glass 

 or other similar factory, may produce an impression of 

 his hand by simply laying the same upon a sensitive sur- 

 face of this kind, the minute traces of mercury in the 

 pores of the skin being amply sufficient to bring about 

 a reduction of the salt, and to produce consequently an 

 imprint of the fingers. In the same way a section of 

 wood exposed to mercury vapours, and afterwards pressed 

 in contact with a sheet of sensitive paper, prints off 

 upon the surface all the rings and markings it possesses, 

 the mercury being deposited in the pores of the wood in 

 a more or less condensed form. 



