338 



NA TURE 



[February 8, 1906 



STIMULUS AND MEMORY. 

 Die Mneme als erhaltendes Prinzip im Wechsel des 

 organischen Geschehens. By Richard Semon. 

 Pp. xiv + 353. (Leipzig: Wilhelm Engelmann, 

 1905.) Price 6s. net. 



LITTLE as it may appear from the title, this work 

 is really an inquiry into some of the remoter 

 effects of stimulation. Thus, every stimulus applied 

 to organic substance — whether that substance be 

 nervous, or not nervously differentiated — produces not 

 only its appropriate reaction, but also an altered con- 

 dition of the substance itself, so that even when the 

 immediate effect of the stimulation has subsided, the 

 second " condition of indifference " is different from 

 the first. The substance may now, for example, 

 readily react to stimuli which before were insufficient 

 to produce any appreciable effect, or it may respond 

 to a stimulus connected only by association with the 

 stimulus usually necessary. It pleases this author to 

 read and group these facts anew, and to apply to 

 them a terminology that will correspond with the 

 novelty of the grouping. Hence he calls the enduring 

 effect of the stimulus an engramm ; the stimulus is 

 said to operate engraphically on the substance, or to 

 produce an engraphic alteration. Again, when 

 stimulus B, differing in quality or quantity from 

 stimulus A, still succeeds with the aid of the engramm 

 in producing a reaction appropriate to A, it is said 

 to operate ecphorically, or the new state of excitation 

 is said to be produced by the ecphory of the engramm. 

 Obviously ordinary memory may be brought under 

 this wide class of phenomena, and the author might 

 have used the term memory to describe these facts"; 

 but, to avoid misunderstanding, he has chosen the 

 term mneme instead. Hence we read of such things 

 as mnemic excitation, e.g. in the case mentioned 

 above when stimulus B is applied. 



The situation is well summed up on p. 89 : — 

 " We recognise the presence of an engramm by the 

 circumstance that for the discharge of the appropriate 

 reaction the appearance of the original unaltered 

 stimulus is no longer necessary, but the appearance 

 either of the original stimulus altered quantitatively 

 or qualitatively, or of a stimulus which works 

 ecphorically on an associated engramm, or the expira- 

 tion of a definite period of time (chronogenous 

 ecphory), or finally the appearance of a definite phase 

 of development in the continuous series of successive 

 generations (phasogenous ecphory)." 



Herr Semon on these lines proceeds to discuss the 

 facts of acclimatisation and instinct, the inheritance 

 of acquired characteristics, and the like, and to trans- 

 late them into his peculiar language. Thus, when 

 according to Mr. Claypole (as reported by Prof. Lloyd 

 .Morgan) young ostriches hatched in an incubator 

 pick up food thrown before them only after someone 

 has " dabbed " with his finger on the ground in their 

 presence, our author's interpretation is that we have 

 here the ecphory of an inherited engramm, an 

 engramm the appropriate reaction of which is peck- 

 ing; the ecphoric stimulus in this case is the return 

 of the primary stimulus (pecking on the part of the 

 mother hen) altered to some extent qualitatively. 

 NO. 1893, VOL. 73] 



The limits of space forbid a full account or 

 discussion of many interesting questions raised by 

 Herr Semon. In the second part of the book he deals 

 with the mutual relations of engramms, their local- 

 isation, the mnemic conditions of excitation, and 

 mnemic homophony. By mnemic homophony is 

 meant " the process by which mnemic excitation and 

 fresh original excitation are, so to speak, made to 

 coincide, and by which each disagreement between the 

 two produces a perceptive reaction." The third part 

 discusses the reality of mnemic processes in " onto- 

 genesis." In the fourth the author deals with various 

 objections, and claims for Mneme that it is a neces- 

 sary preservative principle which protects the trans- 

 formations continually produced by the external world. 

 He claims, also, that it helps us to an understanding 

 of the law of which Haeckel is the unwearying ex- 

 ponent, viz. that the individual passes through the 

 same stages of development as the whole species to- 

 which it belongs. 



The author seems a competent reasoner and 

 observer. His work is interesting and suggestive, 

 and opens a fruitful field for discussion. 



ECONOMY IX THERMAL POWER PLANTS. 

 Commercial Economy in Steam and other Thermal 

 Powei Plants as Dependent upon Physical 

 Efficiency, Capital Charges, and Working Costs. 

 By Prof. Robert H. Smith. Pp. xxiv + 291 ; with 

 numerous diagrams by H. Malcolm Hodson. 

 (London: Constable and Co., Ltd., 1905.) Price 

 24s. net. 



' I 'HE aim of this work is to deduce sufficiently 

 -*- accurate laws for determining the most 

 efficient power plant when all-round economy is 

 taken into account. For this purpose it is necessary 

 to determine a standard of economy, and this is fully 

 discussed in the opening chapter, where a coefficient 

 is defined depending upon the value of the product 

 directly and on the cost and time inversely. The 

 application of this standard to measure the efficiency 

 of production is applied to some examples, and the 

 results of the analyses are considered in detail. After 

 a discussion of the properties of steam, the efficiencies 

 of engines and boilers, and questions of a kindred 

 nature, the author proceeds to deal with the interest- 

 ing question of the cost of various forms of thermal 

 power plant. 



The data for this chapter have been drawn from 

 various sources, principally from makers' catalogues, 

 and are exhibited in graphical form for heat engines 

 by plotting capital or annual costs as ordinates 

 against final cylinder volumes or brake horse-power 

 as abscissae. In this way very interesting relations 

 are established, which can generally be approximately 

 represented by straight-line laws with sufficient 

 accuracy to form a fair estimate of cost. Thus for 

 Crossley gas engines up to 500 horse-power with 

 Dowson gas producers, the capital cost, including the 

 building, is given as 3oo+io-ST, where T is the 



