CHEMISTRY OF THE PROTOPLAST 63 



no one can say whether or no under special conditions, such as existed 

 on the earth before it cooled, or such as are found on other planets, life 

 of a totally different character may not have existed, or in the latter case 

 may not still exist. It is not impossible that there may be organisms in 

 which the place of carbon is taken by silicon, or by some other element. 

 Since the number of compounds in which silicon can replace carbon is 

 relatively small, and since we know of no element which can combine with 

 others in the multifarious ways that carbon does, such life would necessarily 

 be of simpler character, and capable of vital manifestations of much less 

 varied character than is the form of life which the protoplast reveals to us. 

 The fact that we know so little even of our sister planets, and the possibility 

 of the existence on them and elsewhere of elements which are new to us, 

 renders vain all such speculation. 



Sufficient has, however, been said to show that it is a fundamental 

 error to suppose that protoplasm is a definite chemical entity, or that one 

 particular substance is responsible for the vital powers of the whole. 



It has not yet been satisfactorily determined whether, in addition to 

 proteids ; other bodies, such as lecithin, cholesterin l , fats or carbo-hydrates, 

 may not form directly, or in combination with proteids, an essential part 

 of the living protoplast, for a substance may be essential, even though but 

 little of it be present. On the other hand, the constant presence of certain 

 materials does not afford conclusive evidence on this point, for frequently 

 substances are constantly present which do not form an essential part of 

 living protoplasm. 



Our chemical knowledge of the group of bodies known as proteids 

 is as yet very incomplete, and owing to their large and complicated 

 molecules, the variety of possible combinations is much greater than 

 in the group of the carbo-hydrates. It is certain that a very small 

 proportion are as yet known of all the possible proteids and their 

 combinations. Our present knowledge on this point indicates that they 

 are a group in which very trifling stimuli readily produce molecular and 

 other changes, or induce processes of decomposition or polymerization. 

 Hence it is possible that the proteids present in the living cell become 

 disorganized when death takes place, either as the result of contact with 

 substances from which they were separated so long as life was retained -, 

 or because they can exist only under very peculiar and special conditions. 

 No chemical analysis of dead plasma can reveal to us, or give us any 

 information about, proteids of this character ; hence, at present a knowledge 



1 Kossel (Archiv f. Physiologic, 1891, p. 181) concludes that this union is essential. Ou 

 Choltsterin in plants, see Schulze, Zeitschr., f. Physiol. Chemie, 1890, Bd. xiv, p. 512. On Leci- 

 thin, Schultze, Versuchsstat., 1894, Kd. XLIII, p. 307 ; Stocklasa, Ber. d. Chem. Gesellschaft, 1896, 

 p. 2761. 



2 Pfeffer, Oxvd^tionsvorgange in lebcnden Zellen, 1889, p. j?f>. 



