288 APPENDIX 



it is used to designate any reaction which is hastened by a third substance, 

 this third substance not appearing much, if at all, changed in amount at 

 the end of the reaction. Living matter is hence peculiar in the speed with 

 which these hydrolytic, oxidative, reduction, or condensation reactions 

 occur in it; and it owes this property to various substances, catalytic 

 agents, or enzymes, found in it everywhere. Were it not for these sub- 

 stances reactions would go on so slowly that the phenomena of life would 

 be quite different from what they are. Since these catalytic substances 

 are themselves produced by a chemical change preceding that which they 

 catalyze, we might, perhaps, call them the memories of those former chem- 

 ical reactions, and it is by means of these memories, or enzymes, that 

 cells become teachable in a chemical sense and capable of transacting 

 their chemical affairs with greater efficiency. Whether all our memories 

 have some such basis as this we cannot at present say, since we do not 

 yet know anything of the physical basis of memory. 



"Living reactions have one other important pecuUarity besides speed, 

 and that is their ^orderliness.^ The cell is not a homogeneous mixture in 

 which reactions take place haphazard, but it is a well-ordered chemical 

 factory with specialized reactions occurring in various parts. If proto- 

 plasm be ground up, thus causing a thorough intermixing of its parts, it 

 can no longer live, but there results a mutual destruction of its various 

 structures and substances. The orderhness of the chemical reactions is 

 due to the cell structure; and for the phenomena of life to persist in their 

 entirety that structure must be preserved. It is true that in such a ground- 

 up mass many of the chemical reactions are presumably the same as those 

 which went on while structure persisted, but they no longer occur in a 

 well-regulated manner; some have been checked, others greatly increased 

 by the intermixing. This orderliness of reactions in living protoplasm is 

 produced by the speciahzation of the ell in different parts. . . . Thus 

 the nuclear wall, or membrane, marks off one very important cell region 

 and keeps the nuclear sap from interacting mth the protoplasm. Pro- 

 found, and often fatal, changes sometimes occur in cells when an admix- 

 ture of nuclear and cytoplasmic elements is artificially produced by rup- 

 ture of this membrane. Other localizations and organizations are due to 

 the colloidal nature of the cell-protoplasm and possibly to its lipoid char- 

 acter. By a colloid is meant, literally, a glue-hke body; a substance which 

 will not diffuse through membranes and which forms with water a kind 

 of tissue, or gel. It is by means of the colloids of a protein, lipoid, or car- 

 bohydrate nature which make up the substratum of the cell that this 

 localization of chemical reactions is produced; the colloids furnish the 

 basis for the organization or machinery of the cell; and in their absence 

 there could be nothing more than a homogeneous conglomeration of re- 

 actions. The properties of colloids become, therefore, of the greatest 



