430 



Dr. W. Kiihne. On the 



At this point experimental physiological research had to step in, 

 attacking the problem in the same way as it had long before done 

 in the case of the most highly developed contractile structures, the 

 muscles. A muscle behaves so far just like protoplasm that its con- 

 traction does work, which, can only depend on chemical transforma- 

 tions of its own substance, during which potential is converted into 

 kinetic energy ; but it differs in that a distinct impulse from without 

 is needed to set the game going. In normal conditions it receives the 

 initiating impulse from its nerve, and nothing else appears able to 

 take its place, since nothing that might otherwise act upon it, such as 

 the motion of 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. 



ISTow is protoplasm irritable in this sense ? Experiments on ob- 

 jects 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, besides rise of temperature, which 

 ultimately sets all contractile cell- sub stance in maximal contraction — 

 a heat tetanus (4) 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. 



I may be permitted to adduce an example because it illustrates what 

 is typical and essential (5). It is the case of the fresh water Amcebse. 

 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 move- 

 ment, 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 Plas- 

 modium of the Myxomycetes) form several such spheres in part 



