March 28, 1895] 



NATURE 



519 



the current should be kept as nearly uniform as possible, and 

 the readings of the instrument observed at frequent intervals of 

 time. These observations give a curve from which the reading 

 corresponding to the mean current (time-average of the current) 

 can be found. The current, as calculated from the voltameter 

 results, corresponds to this reading. 



The current used in this experiment must be obtained from a 

 battery, and not from a dynamo, especially when the instrument 

 to be calibrated is an electrodynamometer. 



The Volt. 



Definition and Properties of the Cell. — The cell has for its 

 positive electrode, mercury, and for its negative electrode, 

 amalgamated zinc ; the electrolyte consists of a saturated solu- 

 tion of zinc sulphate and mercurous sulphate. The electro- 

 motive force is I '434 volts at 15' C, and between io° C. and 

 25'C.,by the increase of l' C. in temperature, the electro- 

 motive force decreases by o'ooil5 of a volt. 



To set up the Cell. — The containing glass vessel, represented 

 in the accompanying figure, shall consist of two limbs closed at 



bottom and joined above to a common neck fitted with a ground- 

 glass stopper. The diameter of the limbs should be at least 

 2 centimetres, and their length at least 3 centimetres. The 

 neck should be not less than I '5 centimetres in diameter. At 

 the bottom of each limb a platinum wire of about 0*4 millimetre 

 diameter is sealed through the glass. 



To set up the cell, place in one limb pure mercury, and in the 

 other hot liquid amalgam, containing 90 parts mercury and 10 

 parts zinc. The platinum wires at the bottom must be com- 

 pletely covered by the mercury and the amalgam respectively. 

 On the mercury, place a layer one centimetre thick of the zinc 

 and mercurous sulphate paste described in 5. Both this paste 

 and the zinc amalgam must then be covered with a layer of the 

 neutral zinc sulphate crystals one centimetre thick. The whole 

 vessel must then be filled with the saturated zinc sulphate 

 solution, and the stopper inserted so that it shall just touch it, 

 leaving, however, a small bubble to guard against breakage 

 when the temperature rises. 



liefore finally insetting the glass stopper, it is to be brushed 

 round its upper edge with a strong alcoholic solution of shellac, 

 and jtres'^ed firmly in place. 



T^ 



on the nature of muscular 

 contraction:- 



'HE subject of this lecture is an inquiry into '" The Nature of 

 Muscular Contraction." Like all vital phenomena, mus- 

 cular contraction is a most complicated process, composed of 

 mechanical, chemical, thermal, and electrical changes in living 

 matter. Hence it will be our task to become acquainted with 



1 The Croonian Lecture, delivered by Prof. Th. \V. Engelinaan,*at the 

 Royal Society, on March 14. 



NO. 1326, VOL. 51] 



these changes as completely and exactly as possible, and to 

 ascerlain their causal connection. Our inquiry must not be 

 restricted to one special kind of muscle : it will have to extend 

 to all the different forms, for there can be no doubt but that in 

 ail these cases the principle of activity is the same. Nay, it 

 will be necessary to deal even with the other phenomena of so- 

 called contractility, such as protoplasmic and ciliary motion, for 

 all these different types of organic movement, however much 

 they may differ from each other in details, are yet so con- 

 nected by gradual transitions, that, to all appearance, one 

 principle of motion, essentially the same, is applicable to all of 

 them. 



The general mechanical principle on which muscular con- 

 traction is based, will be discovered when we shall have 

 ascertained in what way the power of shortening proceeds 

 from the potential chemical energy which disappears upon 

 stimulation of the muscle. 



There can be no doubt as to the fact that the potential chemical 

 energy of the component parts of muscular substance is alone the 

 ultimate source of this power, for the existence of any other source 

 cannot be proved. The quantity of energy which is imparted 

 to the muscle by the stimulus is too small to be taken into con- 

 sideration. The early opinion that the power required for con- 

 traction was imparted to the muscle through the medium of 

 motor nerves has been refuted by experiments, such as, e.g., on 

 the persistence of contractility after degeneration of the motor 

 nerves, and on the effects of direct artificial stimulation of the 

 muscles ; and it had even been refuted long ere the law of con- 

 servation of energy had thrown its light on the mutual connec- 

 tion between the phenomena of the living organs. 



This law teaches that all the actual energy which appears in 

 the muscle in consequence of stimulation must originate in an 

 equivalent quantity of some other form of energy. 



Now this form of energy is, in fact, given in the muscular 

 substance liable to physiological combustion. The quantity of 

 the latter is not only theoretically sufficient to produce that 

 actual energy, but it has even been proved experimentally that 

 during contraction that material gives birth to combinations 

 such as carbonic acid, in the development of which potential 

 chemical energy must have passed into other forms of energy. 

 As far as the phenomena have been examined quantitatively, 

 they confirm the conclusion that all muscular force must be 

 derived from chemical energy. 



Hence there is no difference about all these points. But with 

 this result we have as yet gained only a basis for the proper 

 solution. So soon you inquire in what way, by what trans- 

 formations, does the mechanical force of contraction arise from 

 chemical energy, difficulties and differences of opinion begin to 

 present themselves. 



A great many physiologists hold, with Pfliiger, Fick, and Chau- 

 veau, that muscular force is a direct manifestation of chemical 

 attraction; others, <•,.;'., Solvay, think that it is produced 

 through the medium of electricity ; others again, following J. 

 R. Mayer, believe that the muscle is a thermodynamic machine, 

 not unlike our caloric or steam engines. 



The Chemiodynamic Hypothesis. — The first hypothesis, ac- 

 cording to which contraction of muscle is a direct manifestation 

 of chemical attraction -we may call it the chemiodynamic hy- 

 pothesis — has to assume ihat the molecules, on the chemical 

 combination of which this contraction is based, are regularly 

 arranged within the contractile substance in such a way as to 

 make them approach each other at their combination in the 

 direction of the axis of the muscular fibres. 



I think that this hypothesis of the identity of chemical at- 

 traction and muscular force meets with a fundamental difficulty 

 in the fact that, in a single contraction, only a relatively 

 infinitesimal part of the muscular substance is chemically 

 active ; 70 to So per cent, of the muscle (.and even more) con- 

 sists of absorbed water, the rest contains substances (albumin, 

 salts, &c.) which, for the greater part, so far as can be proved, 

 are not chemically concerned in the contraction. 



This quantitative composition and this minvte consumption 

 of the active muscle compel us to assume that relatively only 

 very few molecules of the muscular substance can be considered 

 as sources of energy, and of these .again it is generally but a 

 small part that at a cenain moaient perform their function. 



With certain presuppositions we may calculate the quantity 

 of matter through the chemical action of which the amount of 

 actual energy, produced at a certain conti action, must have been 

 generated. 



