46 BLOOD. 



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 cor- 

 puscle as glycogen, but it is very apt, after the death of the corpuscles, to 

 become changed by hydration into some form of sugar, such as maltose or 

 dextrose. 



Lastly, the ash of the white corpuscles is characterized by containing a 

 relatively large quantity of potassium and of phosphates and by being rela- 

 tive 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 dif- 

 ferentiated 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 mag- 

 nesium 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 as 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 replen- 

 ishing 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 purpose of becoming, and is on the way to become living 

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

 changes, 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 as 

 waste. In using the word " living substance,'' however, we must remember 

 that in reality it is not a substance in the chemical sense of the word, but 

 material undergoing a series of changes. 



If, now, we ask the question, which part of the body of the white cor- 

 puscle (or of a similar element of another tissue) is the real living substance, 

 and which part is food or waste, we ask a question which we cannot as yet 

 definitely answer. We have at present no adequate morphological criteria 



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



