THE BASIS OF LIFE 7 



sion, perhaps, of fats, sugars, inorganic salts. But herein lies 

 the biologist's dilemma. He cannot assert that there exists a 

 homogeneous substance, protoplasm. He cannot assert that 

 there exists a definite tectonic grouping of heterogeneous 

 substances which, so long as it is maintained, constitutes a 

 physical basis capable, and alone capable, of exhibiting the 

 phenomena of life. Protoplasm is still a hypothetical sub- 

 stance a name. Truly, in the absence of nitrogen-containing 

 compounds of very complicated chemical constitution there is 

 no life. All living things yield on chemical analysis approxi- 

 mately the same nitrogenous substances. No one can say 

 whether the capacity for living is dependent upon the molecular 

 that is to say, the chemical constitution of the basis, or 

 whether it is dependent upon the arrangement of its molecules, 

 its form. It is even open to question whether instability, the 

 capacity for incessant change, both in chemical composition 

 and in form, be not the condition which differentiates living 

 matter from dead. " Physical basis " is too hard a term for 

 this elusive concept of the matter which exhibits life. 



If it were possible by a process of elimination to ascertain 

 the substances which must be present in protoplasm, the 

 physiologist might formulate a reasonable hypothesis as to the 

 nature of this " basis." But there is no part of any living thing, 

 or, at any rate, no part which is not microscopic in its dimen- 

 sions, which can be pointed out as protoplasm and nothing 

 besides. It is impossible to isolate anything which can be 

 described as pure protoplasm. Nor is it possible, by comparing 

 various tissues which are acknowledged to be rich in protoplasm, 

 to ascertain what chemical substances are common to them all. 



If it were feasible, by analysing a number of specimens of 

 protoplasm, to make sure that, although x is absent from one, 

 y from another, and z from a third, some one thing, P, is always 

 present, then P might be regarded as the physical basis, even 

 though it were evident that P alone was not protoplasm 

 Protoplasm would be P combined with either x, y, or z. 

 Globulins and albumins and other proteins are always present, 

 but in varying proportions ; but it is impossible to make 

 certain that either of these chemical substances is more 

 important than the rest. Nor is it possible to assert of either 

 that it is essential. 



