40 METABOLISM. [BOOK i. 



If, now, we ask the question, which part of the body of the 

 white corpuscle (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 to enable us to judge, 

 by optical characters, what is really living and what is not. 



One thing we may perhaps say ; the material which appears 

 in the cell body in the form of distinct granules, merely lodged 

 in the more transparent material, cannot be part of the real living 

 substance ; it must be either food or waste. Some of these granules 

 are fat, and we have at times an opportunity of observing that 

 they have been introduced into the corpuscle from the surrounding 

 plasma. The white corpuscle as we have said has the power of 

 executing amoeboid movements ; it can creep round objects, 

 envelope them with its own substance, and so put them inside 

 itself. The granules of fat thus introduced may be subsequently 

 extruded or may disappear within the corpuscle; in the latter 

 case they are obviously changed, and apparently made use of 

 by the corpuscle. In other words, these fatty granules are ap- 

 parently food material, on their way to be worked up into the 

 living substance of the corpuscle. 



But we have also evidence that similar granules of fat may 

 make their appearance wholly within the corpuscle ; they are pro- 

 ducts of the activity of the corpuscle. We have further reason 

 to think that in some cases, at all events, they arise from the 

 breaking down of the living substance of the corpuscle, that they 

 are what we have called waste products. 



But all the granules visible in a corpuscle are not necessarily 

 fatty in nature ; some of them may undoubtedly be granules of 

 proteid or allied matter, and it is possible that some of them may 

 at times be of carbohydrate or other nature. In all cases however 

 they are either food material or waste products. And what is 

 true of the easily distinguished granules is also true of other 

 substances, in solution or in a solid form, but so disposed as not to 

 be optically recognised. 



Hence a part, and it may be no inconsiderable part, of the 

 body of a white corpuscle may be not living substance at all, but 

 either food or waste. Further, it does not necessarily follow that 

 the whole of any quantity of material, fatty or otherwise, intro- 

 duced into the corpuscle from without, should actually be built up 

 into and so become part of the living substance ; the changes from 

 raw food to living substance are as we have already -said probably 

 many, and it may be that after a certain number of changes, few 

 or many, part only of the material is accepted as worthy of being 

 made alive, and the rest, being rejected, becomes at once waste 

 matter ; or the material may, even after it has undergone this or 

 that change, never actually enter into the living substance but all 

 become waste matter. We say waste matter, but this does not 



