CHAP, i.] BLOOD. 41 



mean useless matter. The matter so formed may without entering 

 into the living substance be of some subsidiary use to the corpuscle, 

 or as probably more often happens, being discharged from the cor- 

 puscle, may be of use to some other part of the body. We do not 

 know how the living substance builds itself up, but we seem com- 

 pelled to admit that, in certain cases at all events, it is able in 

 some way or other to produce changes on material while that 

 material is still outside the living substance as it were, before it 

 enters into and indeed without its ever actually entering into the 

 composition of the living substance. On the other hand, we must 

 equally admit that some of the waste substances are the direct 

 products of the katabolic changes of the living substance itself, and 

 were actually once part of the living substance. Hence we ought 

 perhaps to distinguish the products of the activity of living matter 

 into waste products proper, the direct results of katabolic changes, 

 and into by-products which are the results of changes effected by 

 the living matter outside itself and which cannot therefore be con- 

 sidered as necessarily either anabolic or katabolic. 



Concerning the chemical characters of the living matter itself 

 we cannot at present make any very definite statement. We may 

 say that proteid substance enters in some way into its structure 

 and indeed forms a large part of it, but we are not justified in 

 saying that the living substance consists only of proteid matter in 

 a peculiar condition. And indeed the persistency with which 

 some representative of fatty bodies and some representative of 

 carbohydrates always appear in living tissue, would perhaps rather 

 lead us to suppose that these equally with proteid material were 

 essential to its structure. Again, though the behaviour of the 

 nucleus as contrasted with that of the cell body leads us to 

 suppose that the living substance of the former is a different kind 

 of living substance from that of the latter, we do not know exactly 

 in what the difference consists. The nucleus as we have seen 

 contains nuclein, which perhaps we may regard as a largely modi- 

 fied proteid ; but a body which is remarkable for its stability, for 

 the difficulty with which it is changed by chemical reagents, 

 cannot be regarded as an integral part of the essentially mobile 

 living substance of the nucleus. 



In this connection it may be worth while again to call attention 

 to the fact that the corpuscle contains a very large quantity indeed 

 of water, viz. about 90 p.c. Part of this, we do not know how much, 

 probably exists in a more or less definite combination with the 

 protoplasm, somewhat after the manner of, to use what is a mere 

 illustration, the water of crystallization of salts. If we imagine a 

 whole group of different complex salts continually occupied in turn 

 in being crystallized, and being decrystallized, the water thus en- 

 gaged by the salts will give us a rough image of the water which 

 passes in and out of the substance of the corpuscle as the result of 

 its metabolic activity. We might call this " water of metabolism." 



