1906.] on The Pkymal Basis of Life. 395 



has developed in many directions. The properties of secretion and 

 absorption, of contractiUty and irrital)ility, have been studied in 

 great detail. The classical tields of physiology, the detailed investi- 

 gation of form, and the anatomy of function have Ijeen continuously 

 worked. But the greatest advance has come in the domain of 

 chemical physiology. Ten years ago this was a scientific No Man's 

 Land, despised by the pure chemist and traversed only in a dis- 

 trustful, amateurish way by the physiologist. Now that is changed : 

 on the one hand a race of physiologists has sprung up who are at the 

 same time expert chemists ; on the other one sees a pure chemist, 

 Emil Fischer, of Berlin, bending all the resources of his great labor- 

 atory in men and materials to the central chemical problem of 

 living matter, the chemical structure of proteid. 



The few pages at my disposal would not hold even a catalogue 

 raisoiinee of the new departures. Therefore it is necessary to select 

 a few problems, and for purposes of contrast I choose not the new 

 but the old, w^hich were agitated half a century ago. 



k.i the outset, however, it is necessary to state certain elementary 

 facts — that there is a unit of living matter called the cell, which 

 everywhere and in all places has recognisably the same structure ; 

 and that all forms of Ufe are divisible into two divisions : those in 

 w^hich the individual and the cell are coterminous — the simple-celled 

 forms ; and those more complex and larger types in which the 

 individual is a cell complex — the multicellular forms. The former 

 are probably the more numerous, but they escape notice by reason of 

 their small size, which is imposed upon them by a law, w^ell nigh 

 without exception, which must strike very deeply into the nature of 

 living matter— namely, that no single unit, no cell, that is, can 

 increase to more than microscopical dimensions. When it reaches 

 the limit of size it becomes unstable, a field of force of a peculiar 

 and special nature is formed within it, and by this field of force the 

 cell is presently rent in twain. 



The basis of this curious limitation of size is not far to seek. 

 Living matter is composed of very large molecules, and substances 

 so built possess certain special properties w4iich mark them off from 

 simpler substances. To them the name of colloids is given, after the 

 type of the class of jellies. Now, a jelly is a curious half-way house 

 between the solid and the liquid states. Like a solid, it is capable of 

 retaining differences of state .- it is rarely of uniform character 

 throughout. The rate of relaxation, as Clerk Maxwell called it, of 

 jellies is slow, much slower than that of simple liquids, much faster 

 than that of true solids. Combined with this characteristic inertia, 

 however, is a degree of molecular mobility sufficient for chemical 

 changes of great velocity. x\ jelly is in this way a meeting-place of 

 extremes, and this it is which enables the colloidal state to manifest 

 life. 



Consider now a small free cell, an infusorian swimming in a way- 



