20 PROTOPLASM AND THE CELL 



opportunity to follow out to any extent their great tendency to the trasn- 

 position and formation of polymeria (chains of atoms), and, with the 

 cooperation of oxygen and afterward of water and salts, to evolve into 

 the self -decomposable albumin, which is living matter." In unlimited 

 time unlimited adaptation might, indeed, be rationally postulated. How 

 great the number of millions of years involved in this particular part of 

 evolution no man can accurately estimate. Now, as well as then, Pfliiger, 

 Hackel, and Verworn suppose it is cyanogen which introduces into living 

 matter its " energetic internal motion," the essential of life, known in 

 physiology as metabolism. (This process is defined below: see page 35.) 

 There is nothing, however, in such a supposition to disprove the con- 

 tinued generation anew of protoplasm today. As will be seen when we 

 discuss a special form of protoplasm, muscle, the degree of heat which 

 may obtain in scattered molecules of a mass of living matter is unlimited. 

 It may be high enough to allow of the production of new protoplasm 

 from these molecules situated here and there in the living matter. The 

 chemi-atomic action, oxidation, may be violent, and yet the relative 

 mass of these molecules, although far too small to effect any considerable 

 amount of living substance, may perhaps be large enough to generate 

 anew a particle of protoplasm endowed with life. 



Other biological thinkers have supposed that there is a molecular 

 union of some sort characteristic of the carbohydrate molecule also, 

 since this seems to be present in every form of protoplasm, however small, 

 as will be further seen below. 



Such, in brief, are the most prominent theories as to the origin of life 

 on the earth. A combination of the last two hypotheses discussed is 

 certainly not unreasonable from any point of view. 



Protoplasm not a Definite Chemical Substance. It is necessary to have 

 one idea in mind continually in studying the nature of protoplasm 

 namely, that it is a morphological substance rather than a definite chemi- 

 cal compound. To explain the meaning of this rather important state- 

 ment, we may well consider what the word protoplasm does not mean. 

 The term is not a physical notion. One does not think of protoplasm 

 as a substance with an unchangeable set of physical properties or qualities, 

 such as, for example, diamond or alcohol. Again, protoplasm is not a 

 definite chemical substance. While it has, of course, some definite 

 chemical composition at any one instant, still that composition is so 

 enormously complex that no chemist can learn it. Its extreme lability 

 or changefulness is a thing entirely characteristic of protoplasm, so much 

 so that we cannot think of it as a chemical substance in the common 

 usage of that term. Protoplasm, again, is not, strictly speaking, an 

 anatomical substance, one with an absolutely definite structure like the 

 femur or the kidney. It is not, finally, a physiological substance, one with 

 a definite set of invariable functions like the eye or the stomachs of 

 cattle. We learn to think of protoplasm as a certain general colloidal 

 sort of living matter with certain characteristics and structure too com- 

 plex to be easily defined. 



