628 



NATURE 



[Oct. 25, 1888 



the blood or changes in its constitution, disturbs its repose. 

 But if we let electric currents traverse the muscle, or if we 

 suddenly change its temperature, or act upon it mechanically or 

 chemically, contractions result which do an amount of work out 

 of all relation to the insignificant impulse ; the means employed 

 only set going the process peculiar to the muscle ; and this is 

 what is meant when we term them stimuli, and the faculty of 

 muscles to react to them irritability. 



Now, is protoplasm irritable in this sense ? Experiments on 

 objects of every kind have answered this affirmatively, and, 

 more than that, have even shown a striking agreement with 

 the irritability of muscle. Of the above-mentioned agents, be- 

 sides rise of temperature, which ultimately sets all contractile 

 cell-substance in maximal contraction — a heat tetanus 1 which 

 disappears with cooling — the electric current has shown itself 

 the most efficient, the stimulus which most surely excites 

 muscles of every kind as well as all nervous matter, and has 

 thence become the most indispensable instrument of physiology. 



1 may be permitted to adduce an example because it illustrates 

 what is typical and essential. 2 It is the case of the fresh-water 

 Amoebae. Every time these organisms, moving like melting and 

 rolling drops, are subjected to an induction shock, they contract 

 almost to a sphere, and assume the spherical form completely if 

 the shocks follow each other at short intervals, being by this 

 means fixed for a longer time in this condition. Feebler shocks, 

 which singly have no effect, become effective by summation 

 when applied in quick succession, just as in the case of muscle. 

 If the movements of the animal by itself are sluggish, on 

 electrical stimulation they are strengthened and accelerated. 

 Thus the stimulation increases the natural movement, and if 

 increased stimulation brings about repose, it is only the apparent 

 repose of prolonged maximal contraction, like that of our 

 muscles when we hold out a weight for some time at arm's 

 length. All protoplasm behaves in this way from whatever 

 source derived. Larger masses which cannot contract to one 

 sphere (as in many plant-cells, or those great cake-like giant 

 masses of the plasmodium of the Myxomycetes) form several 

 such spheres in part connected by thread-like bridges. Every- 

 where the taking on of a figure with smallest surface is the 

 result of stimulation and the expression of augmented con- 

 traction. 3 That which was outstretched becomes shorter and in 

 like measure thicker, just as a muscle swells when it shortens 

 itself. 



Since protoplasm, which either does not move at all sponta- 

 neously or so slowly that we cannot perceive it, reacts in the 

 same way to stimuli, we must in the case of ordinary movements 

 infer the existence of processes originating them either in the 

 interior, i.e. automatic stimuli, or of external processes which 

 had at first escaped us. Whoever sees f >r the first time the 

 action of any one of the simpler independent Protozoa cannot 

 avoid the idea that psychic activity in the strictest sense of the 

 term lies behind it, something like will and design. He sees 

 the elementary being seeking and taking up food, avoiding 

 obstacles, and when touched by foreign objects energetically 

 drawing back, so that he infers sensation also. Possibly he has 

 struck the correct solution — at least we could not refute him — but 

 we should put his deduction to a hard proof if we showed him 

 the same phenomena in the colourless cells of his own blood, or 

 in the protoplasm of a plant-cell ; and if we placed him before 

 the rhythmically contracting cells from the beating heart of a 

 bird's egg incubated barely a couple of days, he would certainly 

 wish with us that the search were for a more material cause, and 

 hope that among them some chemical or physical cause might be 

 found to set up the process. Biology cannot indeed yet claim 

 to have established such causes in explanation of the automatism 

 of protoplasm, but no one will blame the science for continuing 

 the search for them. 



Some causes are already excluded, e.g. light, although there 

 are a few micro-organisms whose movements are excited by it. 4 

 Fluctuations of temperature may also be left out of account. On 

 the other hand, oxygen has a notable influence. 5 Withdrawal 



W. Kiihne, " Untersuchungen iiber das Prot9plasma und die 

 Contraktilitat," Leipzig, 1864, PP- 4 2 > 66, 87, 102. 



2 Kiihne, ibid. p. 30. 



3 Th. W. Engelmann, five years later, confirmed the passage of proto- 

 plasm, especially of Amoeba, to the spherical form on stimulating ; cf. his 

 " Beitrage zur Physiologie des Protoplasmas," Pfliiger Archi-u, vol. ii. 

 1869, p. 315, and " Handbuch der Physiologie, herausg. von L. Hermann," 

 vol. i. p. 367. 



4 Engelmann, " Ueber die Reizung des contraktikn Protoplasma durch 

 plotzliche Beleuchtung," Pjiiiger Archiv, vol. xix. p. 1. 



5 Kiihne, I.e., pp. 50, 67, 88-89, 104-106. The cessation of the so-called 

 sap-stream in the cells of Chmra on excluding the air by oil was observed as 



of the vital air stops all protoplasmic movement, though without 

 killing the cell-body, as is seen from the fact that after the loss 

 of automatism electrical stimulation can supply its place, and 

 that the normal movements return on readmitting the air. 



We might thus consider oxygen the prime mover in automatism, 

 and processes of oxidation its essence, did we not remember that 

 many objects need very prolonged withdrawal of the gas to 

 come completely to rest. This might, however, depend upon 

 the difficulty of removing the last traces of oxygen com- 

 pletely, or it may be that these cannot be removed by the means 

 adopted, but must remain until consumed by the protoplasm 

 itself. 



Since protoplasm is of pap-like softness, and may be in a 

 state of rest or motion at a>>y spot, its exterior limits are just 

 as capable of change as everything within it is capable of 

 quitting its position and taking up any other. Thus the move- 

 ment cannot become more ordered until obstacles confine and 

 direct it. Between the perfected organization of contractile 

 substance in muscle and that of protoplasm capable only of 

 unordered movement, we meet a succession of significant steps 

 hy means of which we can see how the ordering was attained. 

 The first step would seem to consist in the uncommonly wide- 

 spread flagellar and ciliary motion, in which an elastic structure, 

 affixed on one side to the contractile mass, is drawn down or 

 bent by its movement, straightening out again in the rhythmic 

 pauses of repose. A further step, at which the contraction can 

 only take place along an axis, consists in the arrangement of the 

 protoplasm in fine strips wholly or partially surrounded by elastic 

 walls, or again in elastic fibrils being embedded in protoplasmic 

 processes. In this case we have actual primitive muscles before 

 us, of which the most elegant examples are known in the 

 Infusoria among the Vorticellx and Stentores. The movement 

 of these structures is quite like that cf muscle. The strips 

 lengthen and thicken, and they may also be contracted in quick 

 twitches or in a prolonged tetanus, the relaxing, like the stage 

 of diminishing energy of all muscles, always proceeding more 

 slowly than that of the increasing energy before the maximum. 



The muscles of the unicellular Infusoria, no longer doubtful 

 in a physiological sense, show us muscle as a constituent of the 

 cell, and differentiation, without the production of new cells 

 specially endowed for the purpose, taking place in one cell to 

 the extent of elaborating contractile elements determinate in 

 form and precise in work. It is very noteworthy that side by 

 side with these muscular strips provided with highly regulated 

 movement, other protoplasm persists, which continues unin- 

 terruptedly its ordinary unordered movements, while no such 

 unrest is to be remarked in the muscles. On the contrary, these 

 latter are only used from time to time, apparently for attaining 

 distinct objects. We get the impression that the automatism 

 has, as it were, been lost by this portion, so that it must wait 

 for stimuli to reach it from other parts of the cell. If oxygen 

 really applies the first spur to the protoplasm, it has no direct 

 power over the primitive muscle, so that compared with the 

 protoplasm the muscle is endowed with a diminished irritability. 



It has often been said that protoplasm presents the complete 

 set of vital phenomena — assimilation, dissimilation, contractility, 

 automatism, resorption, respiration, and secretion, and even 

 reproduction by dividing. Leaving reproduction on one side, 

 as now disputed, and on good grounds, we can assent to the 

 assertion, and examine which of those functions remain for the 

 products of differentiation. In the case of the muscle, we find 

 it to be all of them with the exception of a single one ; for, 

 while it undoubtedly takes part in nutrition as in respiration and 

 carries on a chemical exchange, all of which are indispensable 

 for contractility, i.e. for its work, and since secretion generalized 

 signifies merely the throwing off of broken-down products, it is 

 wanting only in automatism, that faculty of reacting to certain 

 stimuli, which remained reserved for protoplasm. In this there 

 is nothing opposed to the assumption that protoplasm as opposed 

 to muscle possesses elementary nervous properties. 



The above is sufficient to show the transition to the very 

 highly developed motor apparatus which distinguishes the 

 animal kingdom from almost its lowest stages — I mean the 

 bi-cellular apparatus, which consists of separate cells united 

 only for one purpose, one of which presents the exciting nerve, 

 the other the obedient muscle. 



From past experience we know that division of the nerve, or, 

 more correctly speaking, removal of the nervous cell substance, 



far back as 1774 by Bonaventura Corti : andfurther by Hofmeister in 

 Nitel'a under the influence of reduced atmospheric pressure. Cf. Engelmann 

 in "Handbuch der Physiol, von Hermann," vol. i. Part 1, p. 362. 



