ORGANISM AND MECHANISM 111 



of natural proteins. Even these are being approached, and 

 their synthesis will probably be effected too. 



Chemically regarded, living involves a complex of re- 

 actions in, or associated with the material which we call 

 ' protoplasm ' and some of these reactions can be re- 

 produced apart from the organism altogether. There are 

 oxidations and reductions, hydrations and de-hydrations, 

 fermentings and so on, which taken separately may be 

 mimicked in the laboratory. By freezing tissues, grinding 

 them in a mortar, and thawing and filtering the result, a 

 non-living material can be obtained in which some chemical 

 reactions go on. These can be studied in isolation, and 

 this is one of the everyday methods of bio-chemistry. 

 Similarly, chemical laws are of indispensable assistance in 

 enabling us to understand how the blood carries oxygen and 

 carbon dioxide and how digestive juices change the food in 

 the stomach. 



In the same way it is certain that well-known physical 

 processes occur in the living body. Capillarity plays some 

 part when sap ascends in a tree, and evaporation plays some 

 part when the leaves droop in the summer heat. Surface- 

 tension is illustrated when an egg-cell becomes spherical, 

 and the elasticity of connective tissue when a hen turns 

 suddenly from scanning the sky to inspect a minute seed 

 on the ground at her feet. We illustrate the action of levers 

 when we walk, and the properties of lenses when an image 

 is formed on our retina. All physiologists are agreed that, 

 in the description of bodily functions, the formulae of 

 chemistry and physics carry us some way. 



And just as the fundamental chemical fact, that no in- 

 crease or decrease of matter ever occurs in a closed system, 

 holds true for the living body and its environment, so it 



