5-4 



NATURE 



[March 28, 1895 



ing woald, moreover, account for the slight decrease of mus- 

 ctilar volume observed in s ron» tetaaic coatra:tion. For, 

 according to the experiments of Qaincke, the abiorptim of 

 water by organised bodies generally leads to a slight condensa- 

 tion.' By this condensation farther heat is developed, and 

 this heat might, by raising the temperature of the doubly-re- 

 fractive elements, be partially transformed into me:hanical 

 energy, and in this way contribute totheproiuctioa of muscular 

 force. 



\'et I cannot consider this e.vplanation as sufficient for all the 

 facts. The same argument which in our eyes seems to dispose 

 of the hypothesis of the identity of chemical attraction and 

 muscular force, viz. the infiniiesimally small quantity of sub- 

 stance which is chemically active during a simple contraction, 

 seems to me to present a fundamental difli-ulty here also. It 

 is hard to understand how through a change in the material 

 composition, effected at one infinitesmal point within a soft 

 watery substance, the whole mass should shorten and thicken, 

 u)ih:s thtrt procctiis from the centre of chemical activity a coii- 

 siJerable amount of kinetic energ}' throughout the subitance. 



The microscopic appearances which prove the turgescence 

 of the doubly-refractive elements during a contraction, do 

 not exclude a direct thermo-dynamical effect. For the 

 almost complete identity in the changes of form, and of the 

 optical and mechanical properties which the doubly refrac- 

 tive constituents of all histological elements undergo during 

 chemical and thermal contraction, seems to bear out the 

 hypothesis, that in the thermal shortening of doubly-refractive 

 elements, through the absorption of watery fluid, we get a 

 shifting of solid and liquid substances analogous to that of 

 turgescence. With most of the microscopical appearances, 

 especially the so called fixed contraction waves, we have, more- 

 over, to do with a high degree of tetanic contraction, or even 

 with rigor, in which, on account of the greatly increased 

 chemical action, a chemically-caused turgescence may have 

 combined in a considerable degree with the thermal con- 

 traction. 



Hence, we may conclude that chemical contraction by 

 turgescence of the inotngmala is most likely a constant con- 

 comitant of the thermal contraction of living mu<cle, but that 

 compared with the latter, in a single contraction at least of 

 striated fibres, the former is of little or no consequence as 

 regards the shortening effect. 



Chemiotonus and 'J'hermotonus. — Both'processes will probably 

 also take part in varying proportion in the ionui of muscle, 

 which in some cases will approach more to pure chemiotonus, 

 in others more to pure thcrmotonus. 



Causes of the Relaxation of Atusclc. Theoretical Considera- 

 tions. Conclusion. — With regard to the relaxation of muscle, 

 according to our theory this must be caused either by cooling, 

 or by the withdrawal of water from the doubly-refractive 

 particles. Indeed, we have found that generally doubly- 

 refractive histological elements, even if they be lifeless like our 

 violin strings, lengthen again upon cooling after they have been 

 contracted by heal, and that lliey lengthen upon neutralisation 

 or diffusion, after they have been contacted by absorption at an 

 ordinary temperature. 



In a normal relaxation the muscle seems to return com- 

 pletely to its initial state. Of course its store of energy has 

 diminished in proportion to the quantity of mechanical work 

 and heat which have ])roceeded from it, but, on account of the 

 relatively infinitesimal quantity of substance which is thereby 

 consumed, this return will necessarily seem to be complete even 

 in the case of the isolated muscle. 



When analysing the phenfimena of relaxation more exactly, 

 we shall light on several possibilities, the discussion of which 

 Would be very interesting with regard to the theory of 

 masclc-lire. I shall restrict myself to the phenomena of the 

 relaxation following on thermal contraction. 



Here, in the first place, we might conceive that the doubly, 

 refractive inot.agmata arc ilcstroye 1 in the thermal shortening, 

 so that each of lliem performt(.ls fiinclion once only. The 

 lengilr-ning of the muscular fibrils would then probably be 

 caused solely by the clastic powers of the parts passively ex- 

 tended or compressed by the shortening of the inotagmato. 

 Upon a fresh slimuUlion other inot.n^mnta would, in conie- 

 quciice of the combustion of other thermogenic molecules, be 

 active, peri.sh, &c. Through the activity of the formative matter 



' In the thermal contraction of tendons and strin2» I have not yet been 

 able to coavince myself of .-i decrease in volume. 



NO. 1326, VOX,. 51] 



of the living muscle-fibre, the place of the lost inotagmata would 



I be continually or periodically filled by others, probably through 

 the same process of organic crysiallisation by which during 

 ontogenesis the doubly-refracting particles in the muscle arepro- 



I duced and disposed. 



Against this hypothesis, however, or at least again^^t its general 

 v.alidiiy, various objections m.iybe put forward. I will mention 



] two only of the most important of them. 



There seems to be no doubt but that the doubly-refractive 

 particles of the muscle consist of an albuminous substance, and 



I that they together make up a sensible part of the whole albumin 



' of the muscle fibrils. In that case it would be most improbable 

 that a great increase of muscular work should not at all, or very 



i slightly only, increase the elimination of nitrogen. To account 

 for this, we should have to recur to an auxiliary hypothesis, 

 and assume either that the nitrogenous remainder of ihe de- 

 stroyed inotagma is retained within the body — perhaps in the 

 muscle — for purposes of anabolism, or, which is most improt ■ 

 able indeed, that other organs saved just as much albumin :. 



I was decomposed above the normal quantity duiing the cor.- 

 traction of the muscles. 



A second objection consists in the fact that after heatini; 

 tetanising muscles until they are rigid, the doubly-refractive 

 power of the jarcous elements will be found slill very great. 



The other possibility is that the imiagmata may be preserved, 

 and consequently on cooling may return to their former state, 

 and therefore will do work by shortening as often as we choose. 

 In this case muscle would not only seem to offer, but would 

 ofler in fact, a most striking resemblance to a thermodynamic 

 machine, the solid particles of the framework of which are not 

 destroyed through the chemical process producing the actual 

 energy. No more than such a machine would the muscle 

 require a perpetual renewal of the framework for the con- 

 tinuation of its activity ; it would only want a periodic supply 

 of fresh heating material. 



This representation, as you see, will sufficienily account for 

 the fact, which would otherwise remain surprising, that mus- 

 cular work has such a small influence on the elimination of 

 nitrogen. The facts of microscopic observation also agree 

 with it. 



Hut a further discussion of the two possibilities would lead us 

 too far. The purpose of this lecture was not to record a complete 

 inquiry into all the phenomena of muscular activity. I have 

 wished chiefly to draw attention to a series of facts which I hoKl 

 to be of great importance for a deeper insight into the essence ol 

 muscular contractility, in so far as they prove the existence it 

 certain material dispositions and processes (admitting of closti 

 experimental examination}, by means of which mechanical work 

 may be generated in the muscle by chemical energy. 



THE SNAIL FAUNA OF THE GREATER 

 ANTILLES. 

 T^IIE West Indian Archipelago has long been known to pre- 

 ■*■ sent some interesting problems in the distribution of its land 

 fauna. These peculiarities, it will be remembered, led Wallace 

 to infer the previous existence of a land connection of the 

 greater islands with one another and with the mainUand ; while 

 otiiers have claimed that the islands have always been distinct, 

 and have been colonised by the agency of currents, winds, and 

 other indirect means of dispersni. An interesting contribution 

 on this subject has recently appeared in the form of a study of 

 the distribution of the West Indian land and fresh-water 

 molluscs, by Mr. C. T. Simpson, of the U.S. National 

 Museum, from whose paper we extract Ihe following con- 

 clusions. A considerable portion of the land snail r.auna of tli 

 (jreatcr .'\ntilles >cems to b; ancient and indigenous. Then 

 I appears to be good evidence of a general elevation of the 



Ijrcatcr AntilKan region, probably some lime during the | 

 I Kocene, afier most of the important groups uf snails had come 

 I into existence. .\t this time the larger islands were united, 

 and were connected with Central America by way of Jarnaic 

 and possibly across the ^ ucalan Channel. There was then 

 considerable exchange of species between the two regions. A 

 some time during this elevaiion there was probably a landway 

 from Cuba across the llahaina plateau to the Floridcan .area, 

 over which ccitain groups of Antillean land molluscs crossed. 

 The nioie northern isles of the I.esscr Antilles, if then elevated, 

 have I'lobably been since submerged. Alter the period ol 



