396 Mr. William Bate Hardy [April 6, 



side pool. It displays many activities, it digests in this region of its 

 living l^ody, it maintains a store of starch in that region, in the 

 movements of its parts there is diversity. Both its chemical and 

 physical characters Ijetoken a complexity Avhich show it to be not a 

 homogeneons droplet, bnt, in spite of its minnte size (less than ^ J^ 

 inch), to be heterogeneons. It has a strncture, an architectnre, the 

 coarser features of which we can decipher with the aid of the 

 microscope. 



It is only in the colloidal state that we could have within so small a 

 space so great a diversity of matter, and such differences of chemical 

 potential as must exsist to support the multifarious activities of 

 the living cell, combined with the molecular mobility necessary to 

 give chemical change free play. At the same time this capacity for 

 maintaining differences of state imposes limitations, one of which is 

 that of size. Large molecules can move in the substance of the cell 

 scarcely at all. Therefore, when the size exceeds a certain critical 

 limit, the dynamical balance fails, and internal strains appear of a 

 magnitude great enough to tear the cell apart. On this blending 

 of opposites, on the curious combination of inertia and chemical 

 mobility in the colloidal state, is reared the whole fabric of the 

 dynamics of living matter. 



Each living cell is a machine ; it breathes, taking in oxygen : it 

 feeds, and the food is burnt by the oxygen to chemically simpler 

 bodies. The living cell, like the gas engine, can tap the stores of 

 chemical energy^ — and, like the gas engine, it is an internal combus- 

 tion engine. Now in a power station Avhere electricity is being pro- 

 duced to run a score of trams, there is a steady hum or drone, the 

 varying pitch of which marks the speed of the engine. To the 

 engineer m charge, from long habit, that varying sound speaks of 

 events happening in remote parts of the system. A glance at the 

 clock, and he will tell you that the sound is falling because the 

 engine is adjusting itself to the increased load due to such and such 

 a tram breasting such and such a hill. In the same way, watching 

 the movement of a living cell under the microscope, if we were 

 sufficiently skilled we could refer the continual change in the rate 

 and direction of its mo\ement to temporary inecpialities of tempera- 

 ture, of lighting, or of chemical composition, etc., in the water in 

 which it lives. If we resort to experiment, the effects are obvious : 

 an electric shock causes the irregular amoeba to come to rest as a 

 sphere, a trace of acid slows its movements, of alkali accelerates them. 



These things — the .electric shock, the acid, or the alkali— are what 

 the Ijiologist calls "stinnili,"and by varying their nature or intensity 

 he can control the activity of living matter to a very remarkable 

 extent. 



Let us return for a moment to the amceba. We watch it crawl- 

 ing amid sand, fragments of decayed leaves, and living diatoms, and 

 we notice that of the particles which it eats some are nutritious food. 



