CHAP, ii.] THE CONTRACTILE TISSUES. 153 



the products of muscular metabolism are in the end products of 

 oxidation, but the oxygen appears to be introduced not at the 

 moment of explosion but at some earlier date. As to the real 

 nature of this explosive material we are as yet in the dark ; we do 

 not know for certain whether we ought to regard it as a single 

 substance (in the chemical sense) or as a mixture of more substances 

 than one. We may however perhaps be allowed provisionally to 

 speak of it at all events as a single substance and to call it 'contrac- 

 tile material ' or we may adopt a term which has been suggested and 

 call it inogen. 



We shall have occasion to point out later on, that the living 

 substance of certain cells is able to manufacture and to lodge in the 

 substance of the cell relatively considerable quantities of fat where- 

 by the cell becomes a fat cell, the fat so formed and lodged being 

 subsequently by some means or other discharged from the cell. 

 We shall also have occasion to point out that in a somewhat similar 

 way the living material of certain gland cells manufactures and 

 lodges in itself certain substances which when the cell 'secretes' 

 undergo more or less change and are ejected from the cell. These 

 substances appear to be products of the activity of the living sub- 

 stance of the cell, and to be so related to that living substance that, 

 though discontinuous with it and merely lodged in it they are still 

 capable of being so influenced by it as to undergo change more or 

 less sudden, more or less profound. And we may, resting on the 

 analogy of these fat cells and gland cells, suppose that the living 

 substance of the muscle manufactures and lodges in itself this 

 contractile material or inogen which is capable of being so in- 

 fluenced by the liying substance as to undergo an explosive 

 decomposition. But we here meet with a difficulty. 



The muscular fibre as a whole is eminently a nitrogenous proteid 

 body ; the muscular fibres of the body form the greater part of the 

 whole proteid mass of the body. Moreover the ordinary continued 

 metabolism of the muscular fibre as a whole is essentially a nitro- 

 genous metabolism ; as we shall have to point out later on the 

 muscles undoubtedly supply a great part of that large nitrogenous 

 waste which appears in the urine as urea; the nitrogenous meta- 

 bolism of the muscle during the twenty-four hours must therefore 

 be considerable, and under certain circumstances, as for instance 

 during fever, this nitrogenous metabolism may be still further 

 largely increased. 



On the other hand, as we have already shewn, there can be no 

 doubt that the act of contraction, the explosive decomposition of the 

 inogen, does not increase the nitrogenous metabolism of the muscle. 

 Shall we conclude then that the inogen is essentially a non-nitro- 

 genous body lodged in the nitrogenous muscle substance ? Not 

 only have we no positive evidence of this, but the analogy between 

 contraction and rigor mortis is directly opposed to such a view ; for 

 .it is almost impossible to resist the conclusion that the stuff which 



