CHAP, i.] BLOOD. 41 



the white corpuscles, come certain fats. Among these the most 

 conspicuous is the complex fatty body lecithin. 



In the case of many corpuscles at all events we have evidence 

 of the presence of a member of the large group of carbohydrates, 

 comprising starches and sugar, viz. the starch-like body glycogen, 

 which we shall have to study more fully hereafter. This glycogen 

 may exist in the living corpuscle as glycogen, but it is very apt 

 after the death of the corpuscle to become changed by hydration 

 into some form of sugar, such as maltose or dextrose. 



Lastly the ash of the white corpuscles is characterised by 

 containing a relatively large quantity of potassium and of phos- 

 phates and by being relatively poor in chlorides and in sodium. 

 But in this respect the corpuscle is merely an example of what 

 seems to be a general rule (to which however there may be 

 exceptions) that while the elements of the tissues themselves are 

 rich in potassium and phosphates, the blood plasma or lymph on 

 which they live abounds in chlorides and sodium salts. 



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 1 and a 

 cell body, the nucleus having the general characters described 

 above 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 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 further 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 

 1 The existence of rnultiuuclear structures does uot affect the present argument. 



