392 



NATURE 



\August 21, 1879 



the oxygen contained in the water to disappear. That this 

 phenomenon is a function of the living cell is proved by the 

 fact that, if the yeast be first heated to 60° C. and then placed 

 in the oxygenated water, the quantity of oxygen in the water 

 remains unchanged ; in other words, the yeast ceases to breathe. 



Schiitzenberger has further shown that light exerts no influence 

 on the respiration of the yeast cell— that the absorption of oxy- 

 gen by the cell takes place in the dark exactly as in sunlight. 

 On the other hand, the influence of temperature is well marked. 

 Respiration is almost entirely arrested at temperatures below 10° 

 C, it reaches its maximum at about 40° C, while at 60° C. it 

 again ceases. 



All this proves that the respiration of living beings is identical, 

 whether manifested in the plant or in the animal. It is essentially 

 a destructive phenomenon — as much so as the burning of a piece 

 of .charcoal in the open air, and, like it-, is characterised by the 

 disappearance of oxygen and the formation of carbonic acid. 



One of the most valuable results of the recent careful appli- 

 cation of the experimental method of research to the life 

 phenomena of plants is thus the complete demolition of the 

 supposed antagonism between respiration in plants and that in 

 animals. 



I have thus endeavoured to give you in a few broad outlines a 

 sketch of the nature and properties of one special modification 

 of matter, which will yield to none other in the interest which 

 attaches to its study, and in the importance of the part allocated 

 to it in the economy of nature. Did the occasion permit 1 might 

 have entered into many details which I have left untouched ; 

 but enough has been said to convince you that in protoplasm we 

 find the only form of matter in which life can manifest itself; 

 and that, though the outer conditions of life — heat, air, water, 

 food — may all be present, protoplasm would still be needed, in 

 order that these conditions may be utilised, in order that the 

 energy of lifeless nature may be converted into that of the countless 

 multitudes of animal and vegetable forms which dwell upon the 

 surface of the cirth or people the great depths of its seas. 



We are thus led to the conception of an essential unity in the 

 two great kingdoms of organic Nature — a structural unity, in 

 the fact that every living being has protoplasm as the essential 

 matter of every living element of its structure; and a physio- 

 logical unity, in the universal attribute of irritability which has 

 its seat in this same protoplasm, and is the prime mover of every 

 phenomenon of life. 



We have seen how little mere form has to do with the essential 

 properties of protoplasm. This may shape itself into cells, and 

 the cells may combine into organs in ever-increasing complexity, 

 and protoplasm force may be thus intensified, and, by the 

 mechanism of organisation, turned to the best possible account ; 

 but we must still go back to protoplasm as a naked formless 

 plasma if we would find — freed from all non-essential complica- 

 tions — the agent to which has been assigned the duty of building 

 up structure and of transforming the energy of lifeless matter into 

 that of living. 



To suppose, however, that all protoplasm is identical where 

 no difference cognisable by any means at our disposal can be 

 detected would be an error. Of two particles of protoplasm, 

 between which we may defy all the power of the microscope, all 

 the resources of the laboratory, to detect a difference, one can 

 develop only to a jelly-fish, the other only to a man, and one 

 conclusion alone is here possible — that deep within them there 

 must be a fundamental difference which thus determines their 

 inevitable destiny, but of which we know nothing, and can assert 

 nothing beyond the statement that it must depend on their 

 hidden molecular constitution. 



In the molecular condition of protoplasm there is probably as 

 much complexity as in the disposition of organs in the most 

 highly differentiated organisms ; and between two masses of 

 protoplasm indistinguishable from one another there may be as 

 much molecular difference as there is between the form and 

 arrangement of organs in the most widely separated animals or 

 plants. 



Herein lies the many-sidedness of protoplasm ; herein lies its 

 significance as the basis of all morphological expression, as the 

 agent of all physiological work, while in all this there must be 

 an adaptiveness to purpose as great as any claimed for the most 

 complicated organism. 



From the facts which have been now brought to your notice 

 there is but one legitimate conclusion — that life is a property of 

 protoplasm. In this assertion there is nothing that need startle 



us. The essential phenomena of living beings are not so widely 

 separated from tlie phenomena of lifeless matter as to render it 

 impossible to recognise an analogy between them ; for even 

 irritability, the one grand character of all living beings, is not 

 more difficult to be conceived of as a property of matter than the 

 physical phenomena of radial energy. 



it is quite true that between lifeless and living matter there is 

 a vast difference, a difference greater far than any which can be 

 found between the most diverse manifestations of lifeless matter. 

 Though the refined synthesis of modern chemistry may have 

 succeeded in forming a few principles which until lately had 

 been deemed the proper product of vitality, the fact still remains 

 that no one has ever yet built up one particle of living matter 

 out of lifeless elements — that every living creature, from the 

 simplest dweller on the confines of organisation up to the highest 

 and most complex organism, has its origin in pre-exLstent living 

 matter — that the protoplasm of to-day is but the continuation of 

 the protoplasm of other ages, handed down to us through periods 

 of indefinable and indeterminable time. 



Yet with all this, vast as the differences may be, there is 

 nothing which precludes a comparison of the properties of living 

 matter with those of lifeless. 



When, however, we say that life is a property of protoplasm, 

 we assert as much as we are justified in doing. Here we stand 

 upon the boundary between life in its proper conception, as a 

 group of phenomena having irritability as their common bond, 

 and that other and higher group of phenomena which we desig- 

 nate as consciousness or thought, and which, how'ever inti- 

 mately connected with those of life, are yet essentially distinct 

 from them. 



When the heart of a recently-killed frog is separated from its 

 body and touched with the point of a needle, it begins to beat 

 under the excitation of the stimulus, and we Ijelieve ourselves 

 justified in referring the contraction of the cardiac fibres to the 

 irritability of their protoplasm as its proper cause. We see in 

 it a remarkable phenomenon, but one nevertlieless in which we 

 can see unmistal<able analogies v ith phenomena purely physical. 

 There is no greater difficulty in conceiving of contractility as a 

 property of protoplasm than there is of conceiving of attraction 

 as a property of the magnet. 



When a thought passes through the mind, it is associated, as 

 we have now abundant reason for believing, with some change 

 in the protoplasm of the cerebral cells. Are we, therefore, jus- 

 tified in regarding thought as a property of the protoplasm of 

 these cells, in the sense in which we regard muscular contraction 

 as a property of the protoplasm of muscle? or is it really a pro- 

 perty residing in something far different, but which may yet 

 need for its manifestation the activity of cerebral protoplasm ? 



If we could see any analogy between thought and any one 

 of the admitted phenomena of matter, we should be justified in 

 accepting the first of these conclusions as the simplest,'and as 

 affording a hypothesis most in accordance with the comprehen- 

 siveness of natural laws ; but between thought and the physical 

 phenomena of matter there is not only no analogy, but there is 

 no conceivable analogy ; and the obvious and continuous path 

 which we have hitherto followed up in our reasonings from the 

 phenomena of lifeless matter through those of living matter here 

 comes suddenly to an end. The chasm between unconscious life 

 and thought is deep and impassable, and no transitional pheno- 

 mena can be found by which as by a bridge we may span it 

 over ; for even from irritability, to which, on a superficial view, 

 consciousness may seem related, it is as absolutely distinct as it 

 is from any of the ordinary phenomena of matter. 



It has been argued that because physiological activity must be 

 a property of every living cell, psychica i activity must be equally 

 so, and the language of the metaphysician has been carried into 

 biology, and tlie " cell soul " spoken of as a conception insepar- 

 able from that of life. 



That psychical phenomena, however, characterised as they 

 essentially are by consciousness, are not necessarily coextensive 

 with those of life, there cannot be a doubt. How far back in 

 the scale of life consciousness may exist we have as yet no means 

 of determining, nor is it necessary for our argument that we 

 should. Certain it is that many things, to all appearance the 

 result of volition, are capable of being explained as absolutely 

 unconscious acts ; and when the swimming swarm-spore of an 

 alga avoids collision, and, by a reversal of the stroke of its ciha, 

 backs from an obstacle lying.in its course, there is almost certainly 

 in all this nothing but a purely unconscious act. It is but a case 

 in which we find expressed the great law of the adaptation of 



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