292 



SCIENCE 



[N. S. Vol. XXXVI. No. 923 



only be dealt with by those whose special 

 business it was to study "vital" processes, 

 is passing every day more out of the hands 

 of the biologist and into those of the pure 

 chemist. 



Somewhat more than half a century ago 

 Thomas Graham published his epoch-ma- 

 king observations relating to the proper- 

 ties of matter in the colloidal state: obser- 

 vations which are proving all-important 

 in assisting our comprehension of the prop- 

 erties of living substance. For it is be- 

 coming every day more apparent that the 

 chemistry and physics of the living organ- 

 ism are essentially the chemistry and 

 physics of nitrogenous colloids. Living 

 substance or protoplasm always, in fact, 

 takes the form of a colloidal solution. 

 In this solution the colloids are as- 

 sociated with crystalloids (electrolytes), 

 which are either free in the solution or at- 

 tached to the molecules of the colloids. 

 Surrounding and enclosing the living sub- 

 stance thus constituted of both colloid and 

 crystalloid material is a film, probably also 

 formed of colloid, but which may have a 

 lipoid substratum associated with it (Over- 

 ton). This film serves the purpose of an 

 osmotic membrane, permitting of ex- 

 changes by diffusion between the colloidal 

 solution constituting the protoplasm and 

 the circumambient medium in which it lives. 

 Other similar films or membranes occur in 

 the interior of protoplasm. These films have 

 in many cases specific characters, both phys- 

 ical and chemical, thus favoring the dif- 

 fusion of special kinds of material into and 

 out of the protoplasm and from one part 

 of the protoplasm to another. It is the 

 changes produced under these physical con- 

 ditions associated with those caused by ac- 

 tive chemical agents formed within proto- 

 plasm and known as enzymes, that ef- 

 fect assimilation and disassimilation. Quite 

 similar changes can be produced outside 



the body (in vitro) by the employment of 

 methods of a purely physical and chem- 

 ical nature. It is true that we are not yet 

 familiar with all the intermediate stages of 

 transformation of the materials which are 

 taken in by a living body into the mater- 

 ials which are given out from it. But 

 since the initial processes and the final re- 

 sults are the same as they would be on the 

 assumption that the changes are brought 

 about in conformity with the known laws 

 of chemistry and physics, we may fairly 

 conclude that all changes in living sub- 

 stance are brought about by ordinary 

 chemical and physical forces. 



Should it be contended that growth and 

 reproduction are properties possessed only 

 by living bodies and constitute a test by 

 which we may differentiate between life 

 and non-life, between the animate and in- 

 animate creation, it must be replied that 

 no contention can be more fallacious. In- 

 organic crystals grow and multiply and 

 reproduce their like, given a supply of the 

 requisite pabulum. In most cases for each 

 kind of crystal there is, as with living or- 

 ganisms, a limit of growth which is not 

 exceeded, and further increase of the crys- 

 talline matter results not in further in- 

 crease in size but in multiplication of sim- 

 ilar crystals. Leduc has shown that the 

 growth and division of artificial colloids of 

 an inorganic nature, when placed in an 

 appropriate medium, present singular re- 

 semblances to the phenomena of the growth 

 and division of living organisms. Even so 

 complex a process as the division of a cell- 

 nucleus by karyokinesis as a preliminary 

 to the multiplication of the cell by division 

 — a phenomenon which would prima facie 

 have seemed and has been commonly re- 

 garded as a distinctive manifestation of 

 the life of the cell — can be imitated with 

 solutions of a simple inorganic salt, such 

 as chloride of sodium, containing a suspen- 



