250 THE BODY AT WORK 



separate cluster executing the figure appropriate to its mass, 

 indifferent to the movements of neighbouring groups. But 

 if living protoplasm were of the company, the scene would be 

 one of vastly greater animation ; for now it is the ambition of 

 our dancers to form a single group. To this they can never 

 attain. There is a physical limit to the number of dancers 

 who can hold together while the music carries them in wide 

 sweeps backwards and forwards across the floor. At every 

 gust of wind which bursts through an open doorway a group 

 breaks, to clasp hands again as the wind subsides. Proto- 

 plasm is always on the verge of instability ; always snatching 

 at additional atoms which it draws within its ring ; always 

 shaking off other groups of atoms because the ring is too large 

 to hold together. Touch it, and it falls into simpler combina- 

 tions. Kill it, and it becomes a mixture of organic and in- 

 organic compounds which we know and can name. But as 

 long as it is alive as long as it is protoplasm, that is to say 

 integration and disintegration are occurring. Simultaneous 

 complication and simplification is life. The protoplasm- 

 molecule, if we dare to think of it as a molecule, in the sense 

 in which a chemist uses the term, is always changing. It 

 is its variability which makes stimulation possible. Irritability 

 is a tendency to dissociation under the influence of an external 

 force, with reassociation when the force ceases to act. 



The molecules which protoplasm gathers into itself may be 

 classified under the headings oxygen, foods, water, and in- 

 organic salts. It is the two latter which most affect its state, 

 conferring upon it the capacity of exhibiting the phenomena 

 of life. Water and the ions of salts dissolved in water, electro- 

 lytes, are linked to the other elements of its groups. Striving 

 to find room for more molecules of water and more ions, 

 protoplasm expands. It becomes more mobile and more irri- 

 table ; for irritability and mobility vary as the number of these 

 extraneous groups of atoms which protoplasm is in a position 

 to let drop. As an impulse travels through it they lose their 

 hold, recovering it as they pass the impulse on. This progress 

 towards expansion is the lifeward tendency ; the quickening 

 of activity which leads also to the incorporation of additional 

 atoms of nitrogen-containing substances, and consequent 

 growth. 



