524 



NA TURE 



{Sept. 26, T889 



elertient of living material, is not equivalent to a molecule, how- 

 ever big or complex, but must rather be an arrangement or 

 phalanx of molecules of different kinds. Hence the word tagma, 

 first used by Pfeffer,^bas come to be accepted as best expressing 

 the notion. And here it must be noted that each of the physio- 

 logists to whom reference has been made regards the micellae, 

 not as a mere aggregate of separate particles, but as connected 

 together so as to firm a system, a conception which is in 

 harmony with the view I gave you just now from the side of 

 animal physiology, of catalyzing framework and interstitial 

 catalyzable material. 



To Prof. Sachs, this porous constitution of protoplasm serves 

 to explain the property of vital turgescence — that is, its power 

 of charging itself with aqueous liquid- — a power which Sachs 

 estimates to be so enormous that living protoplasm may, he 

 believes, be able to condense water which it takes into its inter- 

 stices to less than its normal volume. For our present pur- 

 pose it is sufficient for us to understand that to the greatest 

 botanical thinkers, as well as to the greatest animal physio- 

 logists, the ultimate mechanism by which life is carried on is not, 

 as Prof. Sachs ^ puts it, " slime," but "a very distensible and 

 exceedingly fine network." 



And now let us try to get a step further by crossing back in 

 thought from plants to animals. At first sight, the elementary 

 vital processes of life seem more complicated in the animal than 

 in the plant, but they are, on the contrary, simpler ; for plant 

 protoplasm, though it may be structurally homogeneous, is 

 dynamically polyergic — it has many endowments — whereas in 

 the animal organism there are cases in which a structure has 

 only one function assigned to it. Of this the best examples are 

 to be found among so-called excitable tissues, viz. those which 

 are differentiated for the purpose of producing (along with heat) 

 mechanical work, lig'it, or electricity. In the life of the plant 

 these endowments, if enjoyed at all, are enjoyed in common 

 with others. 



By the study, therefore, of muscle, of light organ, and of 

 electrical organ, the vital mechanism is more accessible than by 

 any other portal. About light organs W2 as yet know little, but 

 the little we know is of value ; of electrical organs rather more ; 

 about muscle a great deal. 



To the case of muscle, Engelmann, one of the best observers 

 and thinkers on the elementary questions which we have now 

 before us, has transferred the termmology of IS'ageli and Pfeffer 

 as descriptive of the mechanism of its contraction. Muscular 

 protoplasm differs from those kinds of living matter to which I 

 have applied the term "polyergic," in possessing a molecular 

 structure comparable with that of a crystal in the respect, that 

 each portion of the apparently homogeneous and transparent 

 material of which it consists resembles every other. 



With this ultra-microscopical structure, its structure as investi- 

 gated by the microscope maybe correlated, the central fact being 

 that, just as a muscular fibre can be divided into cylinders by 

 cross-sections, so each such cylinder is made up of an indefinite 

 number of inconceivably minute cylindrical parts, each of which 

 is an epitome of the whole. These, Engelmann, following Pfeffer, 

 'calls ino-tagmata. So long as life lasts each minute phalanx has 

 the power of keeping its axis parallel with those of its neighbours, 

 and of so acting within its own sphere as to produce, whenever 

 it is awakened from the state of rest to that of activity, a fluxion 

 from poles to equator. In other words, muscle, like plant proto- 

 plasm, consists of a stable framework of living catalyzing 

 substance, which governs the mechanical and chemical changes 

 which occur in the interstitial catalyzable material, with this 

 difference, that here the ultra-microscopical structure resembles 

 that of a uniaxial crystal.^ whereas in plant protoplasm there 

 may be no evidence of such arrangement. 



According to this scheme of muscular structure, the contraction, 

 i.e. the change of form which, if allowed, a muscle undergoes 

 when stimulated, has its seat not in the system of tagmata but in 

 the interstitial material which surrounds it, and consists in the 

 migration of that labile material from pole to equator, this being 

 synchronous with explosive oxidation, sudden disengagement of 

 heat and change in the electrical state of the living substance. 

 Let us now see how far the scheme will help us to an under- 

 standing of this marvellous concomitance of chemical, electrical, 

 and mechanical change. 



It is not necessary to prove to you that the discharge of carbon 



' Pfeffer, " Pflanzenphysiologle," p. 12 (Leipzig, rSSi). 

 " Sachs, " Experimental- Ph> siol gi"," p. 443(1865*. 

 3 Briicke, '' V'orlesuiigtn," second edilion, vol. li. p. 497. 



dioxide and the production of heat which we know to be 

 associated with that awakening of a muscle to activity which we 

 call stimulation, are indices of oxidation. If we take this fact 

 in connection with the view that has just been given of the 

 mechanism of contraction, it is obvious that there must be in 

 the sphere of each tagma an accumulation of oxygen and oxi- 

 dizable material, and that concomitantly with or antecedently ta 

 the migration of liquid from pole to equator, these must come 

 into encounter. Let us for a moment suppose that a soluble 

 carbohydrate is the catalyzable material, that this is accumulated 

 equatorially, and oxygen at the poles, and consequently that 

 between equator and poles water and carbon dioxide, the only 

 products of the explosion, are set free. That the process is 

 really of this nature is the conclusion to which an elaborate study 

 of the electrical phenomena which accompany it has led one of 

 the most eminent physiologists of the present time, Prof. 

 Bernstein.^ To this I wish for a moment to ask your attention. 



Prof Bernstein's view of the molecular structure of muscular 

 protoplasm is in entire accordance with the theory of Pfliiger 

 and with the scheme of Engelmann, with this addition, that 

 each ino-tagma is electrically polarized when in a state of rest, 

 depolarized at the moment of excitation or stimulation, and that 

 the axes of the tagmata are so directed that they are always 

 parallel to the surface of the fibre, and consequently have their 

 positive sides exposed. In this amendedrform the theory admits 

 of being harmonized with the fundamental facts of muscle- 

 electricity — namely, that cut surfaces are negative to sound sur- 

 faces, and excited parts to inactive — provided that the direction 

 of the hypothetical polarization is from equator to pole, i.e. that 

 in the resting state the poles of each tagma are charged with 

 negative ions, the equators with positive ; and consequently that 

 the direction of the discharge in the catalyte at the moment that 

 the polarization disappears is from pole to equator. 



Time forbids me even to attempt to explain how this theory 

 enables us to express more consistently the accepted explana- 

 tions of many collateral phenomena, particularly those of electro- 

 tonus. I am content to show you that it is not impossible to 

 regard the three phenomena — viz. chemical explosion, sudden 

 electrical change, and change of form — as all manifestations of 

 one and the same process— as products of the same mechanism. 



In plants, in certain organs or parts in which movement takes 

 place, as in muscles in response to stimulation, the physiological 

 conditions are the same or similar, but the structural very 

 different ; for the effect is produced not by a change of form, 

 but by a diminution of volume of the excited part, and this con- 

 sists not of fibres, but of cells. The way in which the diminu- 

 tion of volume of the whole organ is brought about is by 

 diminution of the volume of each cell, an effect which can 

 obviously be produced by flow of liquid out of the cell. At 

 first sight therefore the differences are much more striking than 

 the resemblances. 



But it is not so in reality, for the more closely we" fix our 

 attention on the elementary process rather than on the 

 extern-al form, the stronger appears the analogy— the more 

 complete the correspondence. The state of turgor, as it 

 has been long called by botanical physiologists, by virtue 

 of which the framework of the protoplasm of the plant 

 retains its content with a tenacity to which I have already referred, 

 is the analogue of the state of polarization of Bernstein. As 

 regards its state of aggregation, it can scarcely be doubted 

 that, inasmuch as the electrical concomitants of excitation of 

 the plant cell so closely correspond with those of muscle, here 

 also the tagmata are cylindrical, and have their axes parallel to 

 each other. Beyond this we ought perhaps not to allow specula- 

 tion to carry us, but it is scarcely possible to refrain from connect- 

 ing this inference with the strea ning motion of protoplasm which 

 in living plant cells is one of the indices of vitality. If, as must 

 I think be supposed, this movement is interstitial, i.e. due to the 

 mechanical action of the moving protoplasm on itself, we can 

 most readily understand its mechanism as consisting in rhyth- 

 mically recurring phases of close and open order in the direction 

 of the tagmatic axes, 



In submitting this hypothesis I do not for a moment forget 

 that the fac's relating to the contractiHty of plant cells have as 

 yet been insufficiently investigated. No one has as yet shown 

 that when the leaf of the sensitive plant falls, or that of the fly- 

 trap closes on its prey, heat is developed or oxidation takes 



' Bernstein, ''Neue Theorie der Erregungsvorgange und electrischen 

 Erscheinungen ap den Nerven- und Muskelfasern," U ntenuchungen ans 

 aem Physiolopich^n Institut {\is.\\<t, i388). 



