The Body-Machine and Its Work 343 



the later Middle Ages began to make out the structure of the 

 organs. Later came a generation which dissected the organs 

 into tissues. Later still, as the microscope improved, the tissues 

 were dissected into cells, and the whole life of the organism was 

 resolved into the co-operative life of millions of these units. But 

 we now know that the secrets of the life of the cell lie partly in 

 the molecules which compose the cells, and these are beyond the 

 range of the most powerful microscope. We must wait and be 

 grateful for what we know. Science never rests. On the very 

 day on which I am writing this page the press announces the 

 discovery of a new microscope, which takes us at a bound deeper 

 into the mysteries of living nature! 



Meantime, science has shown us that the muscular system 

 is an automatic living mechanism of the most wonderful kind. 

 To every muscle the arteries bear their streams of food and 

 oxygen, the muscle-cells select their diet, and the veins take away 

 the waste-products. On every muscle there are also the fine 

 endings of some nerve from (generally) the spinal cord, and at 

 the proper moment a discharge along the nerve causes the whole 

 mass of the cells or fibres in a muscle to contract simultaneously 

 and lift the bone to which the muscle is attached. The nerve- 

 impulse itself is slight. It is merely like a match set to the 

 great energy stored up like powder in the muscle. But when 

 we remember the number of muscles needed for a single har- 

 monious action we bring fifty-four into play at each step in 

 walking, and there are about 300 muscles concerned when we 

 walk the delicacy of their adjustment, the precise degree of 

 action needed in each, we cannot but marvel at the ceaseless 

 regularity and correctness of this unconscious play of muscle and 

 nerve and nerve-centre. We can say only that it is broadly and 

 beautifully illluminated by the story of evolution a slow advance 

 during millions of years, during which every individual with a 

 defect is sifted out and every improvement means longer survival 

 in the struggle for life. 



