MUSCLE 251 



The opposite tendency is deathwards. Protoplasm drops 

 extraneous groups of atoms ; retires into itself ; loses irritability ; 

 settles down to rest. 



The molecules of proteins exhibit a property which appears 

 to pertain in some degree to living matter also. When their 

 relation to the water in which they are dissolved and the electro- 

 lytes which it contains is disturbed, they appear to go out of 

 solution, they coagulate. This disturbance is brought about 

 in all proteins by heat ; in some it is the result of altering the 

 amount of salt in the water in which they are dissolved. 

 Coagulation in protoplasm is the prelude to death ; but it 

 would appear that a step in this downward path is taken 

 whenever an impulse is conducted. Coagulation is due to the 

 clustering of the molecules of a protein. When protoplasm 

 drops electrolytes and water its molecules cluster in some 

 degree, regaining their independence and reattaching their 

 accessory groups of atoms as the cause which drove them to 

 make for safety passes by. 



Our conception not of life, but of " the physical basis of 

 life," may be very wide of the mark. The account given above 

 is intended as little more than a hint of the lines along which 

 thought is travelling at the present time. The reader must not 

 regard it as a serious attempt to present in detail the views 

 of any of the workers who are endeavouring to apply the 

 results of recent discoveries in molecular physics to the solu- 

 tion of problems in the chemistry of living matter. There can, 

 however, be little doubt but that we are on the eve of further 

 advances which will secure data upon which it will be legitimate 

 to construct hypotheses. At present it would be unreasonable 

 to do more than indicate the direction from which it may be 

 hoped that light will shine. 



A stimulus is a change of circumstance rather than a transient 

 disturbance. When an electric current is thrown into it, proto- 

 plasm dissociates parts with something. It instantly re- 

 associates. The continued passage of the electric current does 

 not maintain it in a dissociated condition. When the current 

 is cut off, the sudden change again acts as a stimulus. Within 

 limits, the efficiency of an electric stimulus varies as its sud- 

 denness. Similarly with all other stimuli to which protoplasm 

 responds : crushing, burning, chemical decomposition, are 



