NATURE OF PROCESS. 89 



condition of tissue. But no instance is known in which 

 any lifeless substance takes up another lifeless substance 

 differing from it in composition, and converts this last into 

 matter like itself, as occurs, for example, when a simple 

 gelatin-yielding texture increases in amount, although sur- 

 rounded by an albuminous material only in which no trace 

 of gelatin-yielding substance can be detected. 



In the hope of ascertaining the essential nature of the 

 nutrient process, we must not limit ourselves to the con- 

 sideration of the phenomena occurring in the fully-formed 

 organisms of man and vertebrate animals, in which the 

 nutrient blood plays so important a part; but we must 

 extend our observation to plants and the lower organisms, 

 some of which consist of extremely minute independent 

 masses of matter. Many facts lead to the conclusion that 

 the nutritive process is, at least in its essential nature, the 

 same in all cases ; and whatever meaning be assigned to 

 the term, it ought to apply equally to the lowest simplest 

 forms and to the highest and most complex. 



A simple living organism takes up a quantity of nutrient 

 matter and increases in weight. Having reached a certain 

 size portions may be detached, and each of these, after 

 absorbing nutrient matter, grows and gives rise to others. 

 In this case the nutrient pabulum is converted into living 

 matter, and as a result of nutrition there is an enormous 

 gain in weight. But, on the other hand, living bodies may 

 take up a considerable quantity of nutrient matter without 

 altering in weight, and indeed some, in spite of being 

 well supplied with nourishment, actually lose weight. The 

 new matter taken up may exactly compensate for old 



