68 PHYSIOLOGY 



were a mere congeries of cells. There come thus to 

 co-exist the lime-hardened tissues of our bones, the con- 

 tractile cells of our muscles, the conductive cells of our 

 nerves, and so forth. 



And more than that, the living laboratory of the cell 

 itself manufactures even the medium in which the cells 

 are immersed, not only the fibrous and calcareous frame- 

 work, but the very saps and juices of the body. We are 

 learning from pathology that every species of animal 

 produces an internal medium, un milieu interne, specific 

 to itself. The difference between the child that, recovering 

 from some disease, has become immune to that disease, 

 and the child that, not having suffered, is not immune, 

 seems perhaps chiefly expressed as a change in this 

 ' internal medium ' of its body. From this point of view, 

 the processes of the body fall into two categories, those 

 within the cells and those within the body but outside 

 its cells in its intercellular material. 



And these two are connected by a third, namely by 

 processes connected with cell boundaries. These boun- 

 daries limit more or less stringently separate fields of 

 chemical operation : by them spheres of influence for 

 ferment action are confined, osmotic pressures are banked 

 up, ions are checked or sifted, electrical charges are 

 accumulated, and so on. For instance, osmotic energy 

 manifests itself when a soluble substance finds itself 

 unequally distributed in a solvent. If in the living cell 

 disintegration of complex substances go on under the 

 influence of stimuli, in proportion as the number of 

 molecules increases and as the limiting layer of the 

 cytoplasm obstructs their passage osmotic pressure in 

 the cell will rise. Water enters the cells. In proportion 

 as the surface of separation is permeable molecules of 

 chemical products of disintegration diffuse from the cell. 



