PROTOPLASMIC STRUCTURE 29 



use of the expression " vital force" in its old sense. So numerous are the 

 reagents and so numberless their reactions in certain organs, if not in 

 every one, and in all protoplasm, that it seems almost as if there must be 

 some unifying and controlling force, some principle behind and beneath 

 them characteristic of life. If there is such a principle (and it is doubted 

 by some), it would surely be as much inherent in the proteids of organ- 

 isms as elsewhere. Perhaps, as Pfliiger supposes, it would be there alone, 

 or, as is more likely, in an atomic structure combined of proteids, lecithin, 

 carbohydrates, the inorganic salts of several metals, etc., in one great 

 ever-changing adaptable combination well meriting the title of the vital 

 molecule. In no place, however, are conjectures more out of place than 

 in text-books of science. We must hasten to declare, therefore, that 

 about the actual composition and spatial arrangement of the molecule 

 of proteid we know nothing and we could certainly not know less about 

 a hypothetical " vital molecule/' built on a nucleoproteid as a basis. 

 That air of pervading mystery for which the term " vital force" still 

 stands is likely to continue until methods of chemical analysis new and 

 more delicate by far than those in present use are devised and put in 

 practice on living protoplasm the enlightening science, not yet born, of 

 real cytochemistry. 



The definite chemistry of proteids has not advanced sufficiently to 

 allow of any sort of agreement concerning them save that they contain 

 carbon, hydrogen, oxygen, nitrogen, and sulphur, there being disagree- 

 ment even as to the universal presence of phosphorus. The different 

 proteids or albumins (we use the terms as synonymous) have not been 

 identified with sufficient accuracy, so that a single classification is in use 

 the world over. Compare in this respect the chemistry of the saccharides 

 or of the glycerides with that of the proteids, and it is obvious how 

 arbitrary any one classification of the latter must be. The following 

 table is a common arrangement of the albuminous compounds as well as 

 of the others which, so far as isolated, combine to make up protoplasm. 

 It is unlikely that all of these are contained in every organism, however 

 low, although functional representatives of them are probably so con- 

 tained. These substances are technically known as the proximate 

 principles of the animal body. The more promptly and permanently 

 the names, relations, and functions of the substances in this table become 

 familiar to the student, the easier and the more intelligible to him will be 

 the essential composition and functions of animals. 



As is seen in the following table, the proteids of the bodies of animals 

 may be assumed to fall under six general classes: albumins, globulins, 

 nucleoproteids, chromoproteids, glucoproteids, and enzymes (unorgan- 

 ized " ferments," which may not after all prove to be proteids). Into the 

 chemical nature and differentiation of these, as into their varieties, it is 

 not our province to go, for that is the domain of another science than 

 physiology namely, of biochemistry. All that we desire at present is 

 to understand the structure and composition of protoplasm as the basis 

 of vital phenomena. 



