THE BASIS OF LIFE 25 



bodies which it contains. If the windows of a house were 

 endowed with the power of spontaneously enlarging, the walls 

 would be crushed. They would bulge, break, tumble. The 

 matrix of cartilage offers as little resistance to the enlargement 

 of the cells which it encloses as the plasma of blood to the 

 multiplication of blood-corpuscles. It grows with the cell- 

 bodies, and must be considered as divisible into areas, each 

 of which is the periphery of a cell. Muscle is alive. So, too, 

 are bone, teeth, hair, nails. But as we proceed outwards we 

 find the quality of aliveness growing less and less apparent, 

 until at last we acknowledge that it is unrecognizable. Vibra- 

 tions diminish in amplitude and in rapidity, until the material 

 of which the body is made appears to be at rest. 



Biologists apply the term " protoplasm " to the most living 

 substance of which plants and animals are composed. It may 

 be that there is an entity, protoplasm. It may be that in 

 certain situations this exists in an unmixed state. It may be 

 that the degree of aliveness of a tissue or constituent part of a 

 tissue varies as the quantity of protoplasm which it contains. 

 The tendency of protoplasm to dispose itself in a reticulum in 

 the meshes of which other substances accumulate favours such 

 a view. The cells of the deeper layers of the skin are rich in 

 it. The superficial layers are composed chiefly of keratin. 

 It is possible that the network opens out, and its strands grow 

 thinner and thinner, as keratin accumulates. But it cannot 

 be demonstrated that this is the case. There is no completely 

 satisfactory reason for concluding that the life of a cell of the 

 skin resides in its protoplasmic network, while its keratin is 

 inert. 



Many attempts have been made to prove that living cells 

 contain something which dead cells do not contain ; but no 

 evidence which will bear sifting has, as yet, been adduced in 

 support of this thesis. 



