CHAP, i.] BLOOD. 39 



exceptions), that while the elements of the tissues themselves are 

 rich in potassium Mini phosphates, the blood plasma or lymph <>n 

 which they live abounds in chlorides and sodium salts. 



i> 30. In the broad features above mentioned, the white blood 

 corpuscle may be taken as a picture and example of all living 

 tissues. If we examine the histological elements of any tissue, 

 whether we take an epithelium cell, or a nerve cell, or a cartilage 

 cell, or a muscular fibre, we meet with very similar features. 

 Studying the element morphologically, we find a nucleus * and a 

 cell body, the nucleus having the general characters described 

 ahiive with frequently other characters introduced, and the cell 

 body consisting of at least more than one kind of material, the 

 materials being sometimes so disposed as to produce the optical 

 effect simply of a transparent mass in which granules are imbedded, 

 in which case we speak of the cell body as protoplasmic, but at 

 other times so arranged that the cell body possesses differentiated 

 structure. Studying the element from a chemical point of view 

 we find proteids always present, and among these bodies identical 

 with or more or less closely allied to such proteids as globulin and 

 myosin, we generally have evidence of the presence also of fat of 

 some kind and of some member or members of the carbohydrate 

 group, and the ash always contains potassium and phosphates, 

 with sulphates, chlorides, sodium and calcium, to which may be 

 added magnesium and iron. 



We stated in the Introduction that living matter is always 

 undergoing chemical change ; this continued chemical change we 

 may denote by the term metabolism. We furthef urged that so 

 long as living matter is alive, the chemical change or metabolism 

 is of a double kind. On the one hand, the living substance is 

 continually breaking down into simpler bodies, with a setting free 

 of energy ; this part of the metabolism we may speak of as made 

 up of katabolic changes. On the other hand, the living substance 

 is continually building itself up, embodying energy into itself and 

 so replenishing its store of energy ; this part of the metabolism 

 we may speak of as made up of anabolic changes. We also urged 

 that in every piece of living tissue there might be (1) the actual 

 living substance itself, (2) material which is present for the pur- 

 pose of becoming, and is on the way to become, living substance, 

 that is to say, food undergoing or about to undergo anabolic 

 cluinges, and (3) material which has resulted from, or is resulting 

 from, the breaking down of the living substance, that is to say, 

 material which has undergone or is undergoing katabolic changes, 

 and which we speak of under the general term ' waste.' In using 

 the word " living substance," however, though we may for con- 

 venience sake speak of the really living part as a substance, we 

 may repeat that in reality it is not a substance in the chemical 

 sense of the word, but material undergoing a series of changes. 



1 The existence of multiiiuclear structures does not affect the present argument. 



