THE SIDE-CHAIN THEORY 145 



It is, if I may so express it, the fundamental the essential 

 conception of the constitution of living matter; it follows 

 logically and inevitably the postulate of assimilation and growth. 

 Whether we agree, with the majority, to distinguish between 

 the idioplasm and the cytoplasm of the cell, or prefer to speak 

 simply of protoplasm, it must, I think, be recognized by all that 

 we are bound to assume for the process of assimilation and, 

 again, in order to explain the variation in structure and pro- 

 perties of the various cells of the organism that there is a 

 central basal substance to which become linked more or less 

 permanently, or more or less temporarily, those other secondary 

 substances, which, not in themselves protoplasm, modify the 

 constitution of the protoplasm as a whole. And these secondary 

 substances, we see, are necessary for the full manifestation of 

 the properties of that protoplasm. -This conception is, I acknow- 

 ledge, difficult to harmonize with the prevalent elementary 

 conceptions of chemical action and chemical constitution ; but 

 it is, nevertheless, essential for the physiologist and unavoidable. 

 What is more (for I do not pretend to be a chemist), I learn that 

 it is not opposed to the more recent deductions of the chemists 

 concerning the nature and properties of the more complex 

 carbon derivatives. In other words, it is by no means heterodox 

 from an advanced chemical standpoint. 



Accepting this view, it is not necessary to regard the mole- 

 cules of idioplasm as at all times presenting their completed 

 structure, with every side-chain attached. On the contrary, 

 we are free to conceive the molecules being laid down and being 

 transmitted in a relatively simple form, some of the side-chains 

 only becoming attached when the molecules are brought into 

 certain particular relationships with their surroundings. It is 

 not necessary, for example, to hold that already in the ovum 

 there is idioplasm identical in structure with that eventually 

 present in the muscle fibres or nerve-cells developed from that 

 ovum. Rather we must hold that in the ovum there is one 

 common idioplasm of simple type, to which, when distributed 

 in the various cells derived from that ovum, different side-chains 

 become attached, according to the relationships assumed by 

 those cells, so that the cells of different orders are controlled 

 and formed around protoplasmic or idioplasmic molecules com- 

 posed of those central rings plus varying series of side-chains. 



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