Sept. 26, 1889] 



NATURE 



525 



place, but it does not seem to me very rash to anticipate that if it 

 were possible to make the experiment to-morrow it would be 

 found to be so. 



I have thus endeavoured (building on two principles in physio- 

 logy, firstly that of the constant correlation of mechanism and 

 action, of structure and function, and secondly the identity of 

 plant and animal life both as regards mechanism and structure ; 

 and on two experimentally ascertained elementary relations, 

 viz. the relation of living matter or protoplasm to water on the 

 one hand, and to oxygen and food on the other) to present to you 

 in part the outline or sketch of what might, if I had time to 

 complete it, be an adequate conception of the mechanism and 

 process of life as it presents itself under the simplest con- 

 ditions. To complete this outline, so far as I can to-day, 

 I have but one other consideration to bring before you, one 

 which is connected with the last of my four points of departure 

 — that of the relation of oxygen to protoplasm, a relation which 

 springs out of the avidity with which, without being oxidized or 

 even sensibly altered in chemical constitution, it seizes upon oxygen 

 and stores it for its own purposes. The consideration which this 

 suggests is that if the oxygen and oxidizable material are con- 

 stantly stored, they must either constantly or at intervals be dis- 

 charged, and inasmuch as we know that in every instance 

 without exception in which heat is produced or work is done, 

 these processes have discharge of water and of carbon dioxide 

 for their concomitants, we are justified in regarding these dis- 

 charges as the sign of expenditure, the charging with oxygen as 

 the sign of restitution. In other words, a new characteristic of 

 living process springs out of those we have already had before 

 us — namely, that it is a constantly recurring alternation of op- 

 posite and complementary states, that of activity or discharge, 

 that of rest or restitution. 



Is it so, or is it not ? In the minds of most physiologists the 

 distinction between the phenomena of discharge and the pheno- 

 mena of restitution [Er/iolitng] is fundamental, but beyond this, 

 unanimity ceases. Two distinguished men, one in Germany and 

 one in England — I refer to Prof. Hering and Dr. Gaskell — have 

 taken, on independent grounds, a different view to the one above 

 suggested, according to which, life consists, not of alternations 

 between rest and activity, charge and discharge, loading and 

 exploding, but between two kinds of activitj', two kinds of 

 explosion, which differ only in the direction in which they act, 

 in the circumstance that they are antagonistic to each other. 



Now when we compare the two processes of rest, which as 

 regards living matter means restitution, and discharge, which 

 means action, with each other, they may further be distinguished 

 in this respect, that, whereas restitution is autonomic, i.e. goes 

 on continuously like the administrative functions of a well-ordered 

 community, the other is occasional, i.e. takes place only at the 

 suggestion of external influences ; that, in otlier words, the con- 

 trast between action and rest is (in relation to protoplasm) 

 essentially the same as between waking and sleeping. 



It is in accordance with this analogy between the alternation 

 of waking and sleeping of the whole organism, and the corre- 

 sponding alternation of restitution and discharge, of every kind 

 of living substance, that physiologists by common consent use 

 the term Stimulus {Ileiz, Prikkeling), meaning thereby nothing 

 more than that it is by external disturbing or interfering influence 

 of some kind that energies stored in living material are (for the 

 most part suddenly) discharged. Now, if I were to maintain 

 that restitution is not autonomic, but determined, as waking is, 

 by an external stimulus — that it differs from waking only in the 

 direction in which the stimulation acts, i.e. in the tendency 

 towards construction on the one hand, towards destruction on 

 the other — I should fairly and as clearly as possible express the 

 doctrine which, as I have said, the two distinguished teachers I 

 have mentioned, viz. Dr. Gaskell ^ and Prof Hering, have 

 embodied in words which have now become familiar to every 

 student. The words in question, "anabolism," which being 

 interpreted means winding up, and " catabolism," running down, 

 are the creation of Dr. Gaskell. Prof. Hering's equivalents for 

 these are "assimilation, "which, of course, means storage of oxygen 

 and oxidizable material, and " disassimilation," discharge of these 

 in the altered form of carbon dioxide and water. But the point 

 of the theory which attaches to them lies in this, that that 

 wonderful power which living material enjoys of continually 

 building itself up out of its environment, is, as I have already 

 suggested, not autonomic, but just as dependent on occasional 



' See Gaskell in Ltidmig's Festschrift, AnA Hering, " Zur Theorie der 

 Vorgange in der lebendigen Substanz,"pp. 1-22 (Prag, 1888). 



and external influences or stimuli, as we know the disintegrating 

 processes to be ; and accordingly Hering finds it necessary to 

 include under the term stimuli not only those which determine 

 action, but to create a new class of stimuli which he ca.\\5 Assimi- 

 latiotis-Reize, those which, instead of waking living mechanism 

 to action, provoke it to rest. 



It is unfortunately impossible within the compass of an address 

 like the present to place before you the wide range of experi- 

 mental facts which have led two of the strongest intellects of our 

 time to adopt a theory which, when looked at a priori, seems so 

 contradictory. I must content myself with mentioning that 

 Hering was led to it chiefly by the study of one of the examples 

 to which I referred in my introduction — namely, the colour-dis- 

 criminating functions of the retina ; Dr. Gaskell by the study of 

 that very instructive class of phenomena which reveal to us that 

 among the channels by which the brain maintains its sovereign 

 power as supreme regulator of all the complicated processes 

 which go on in the different parts of the animal organism, there are 

 some which convey only commands to action, others commands 

 to rest, the former being called by Gaskell catabolic, the latter 

 anabolic. To go further than this would not only wear out your 

 patience but would carry me beyond the limits I proposed to 

 myself, viz. the mechanism of life in its simplest aspects. I there- 

 fore leave the subject here, adding one word only. The distinc- 

 tion which has suggested to their authors the words on which 

 I have been commenting is a real one, but it implies 

 rather the interference with each other of the simultaneous 

 operation of two regulating mechanisms, than an antagonism 

 between two processes of opposite tendencies carried on by the 

 same mechanism ; or, putting it otherwise, that the observed 

 antagonism is between one nervous mechanism and another, 

 and not between two antagonistic functions of the same living 

 material. 



Without attempting to recapitulate, I have a word to say by 

 way of conclusion on a question which may probably have 

 suggested itself to some of my audience. 



I have indicated to you that although scientific thought does 

 not, like speculative, oscillate from side to side, but marches 

 forward with a continued and uninterrupted progress, the stages 

 of that progress may be marked by characteristic tendencies ; 

 and I have endeavoured to show that in physiology the questions 

 which concentrate to themselves the most lively interest are 

 those which lie at the basis of the elementary mechanism of 

 life. 



The word Life is used in physiology in what, if you like, may 

 be called a technical sense, and denotes only that state of change 

 with permanence which I have endeavoured to set forth to yor. 

 In this restricted sense of the word, therefore, the question 

 " What is Life ? " is one to which the answer is approachable ; 

 but I need not say that in a higher sense — higher because it 

 appeals to higher faculties in our nature — the word suggests 

 something outside of mechanism, which may perchance be its 

 cause rather than its effect. 



The tendency to recognize such a relation as this is what we 

 mean by vitalism. At the beginning of this discourse I referred 

 to the anti-vitalistic tendency which accompanied the great 

 advance of knowledge that took place at the middle of the 

 century. But even at the height of this movement there was a 

 reaction towards vitalism, of which Virchow,^ the founder of 

 modern pathology, was the greatest exponent. Now, a genera- 

 tion later, a tendency in the same direction is manifesting itself 

 in various quarters. What does this tendency mean ? It has 

 to my mind the same significance now that it had then. Thirty 

 years ago the discovery of the cell as the basis of vital function 

 was new, and the mystery which before belonged to the organism 

 was transferred to the unit, which while it served to explain 

 everything was itself unexplained. The discovery of the cell 

 seemed to be a very close approach to the mechanism of life, 

 but now we are striving to get even closer, and with the same 

 result. Our measurements are more exact, our methods finer ; 

 but these very methods bring us to close quarters with pheno- 

 mena which, although within reach of exact investigation, are as 

 regards their essence involved in a mystery which is the more 

 profound the more it is brought into contrast with the exact 

 knowledge we possess of surrounding conditions. 



If what I have said is true, there is little ground for the 

 apprehension that exists in the minds of some that the habit of 



' Virchow, "Alter und Neuer Vitalismus," Atchiv fiir pathol. Anat 

 1856, vol. ix. p. I. See also Rindfleisch, " Artzliche Philosophic," pp. lo-i 

 Wurzburg, 1888). -v 



