42 METABOLISM. [BOOK i. 



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, though we may for convenience sake speak of 

 it as a substance, we must remember that in reality it is not a 

 substance in the chemical sense of the word, but material under- 

 going a series of changes. 



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. Many 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 apparently 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 proteid granules, 

 and it is possible that some of them may at times be of carbo- 

 hydrate 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 re- 

 cognised. 



