14 THE BODY AT WORK 



concerned in this process. If a bird be fed upon urea, or even 

 upon various salts of ammonia, its liver will change them into 

 uric acid. Lactate of ammonia is the nitrogen-containing com- 

 pound with which the liver has normally to deal. It can 

 handle almost any other combination of nitrogen with equal 

 ease. In the protoplasm of the liver the atoms in the molecule 

 of lactate of ammonia are rearranged. The molecules are con- 

 densed ; water is set free ; oxidation occurs. It seems almost 

 as if molecules, when in contact with protoplasm, lose their 

 individuality. Their atoms fall into new groups. Chains 

 which the chemist finds so difficult to break chains from 

 which he can remove a link only by insinuating another and 

 a stronger are, when in contact with protoplasm, groups of 

 isolated links. The links rearrange themselves. They join 

 into new circlets, larger, smaller, more open, closer. As grains 

 of sand on a metal plate group themselves in harmony with 

 the vibrations caused in the plate by drawing a violin bow 

 across it, so the atoms answer to the forces which set proto- 

 plasm vibrating. There is no waste of force. The chemist 

 may need to enclose sawdust and lime in a crucible heated in 

 an electric furnace if he wishes to compel them to combine as 

 carbide. He supplies energy enormously in excess of the 

 amount which the new compound will lock up. Under the 

 influence of protoplasm the reactions which occur are exactly 

 proportional to the amount of energy supplied. Or, if it be a 

 reaction by means of which energy is set free, it occurs spon- 

 taneously. No energy is absorbed in setting it going. All 

 the energy liberated is effective. The chemist very frequently 

 needs to heat a substance in order to cause it to decompose, 

 even though it be falling from a less stable to a more stable 

 state. 



Vital chemistry and mineral chemistry are so widely different 

 in their methods that one is tempted to think of them as 

 different in kind. We find it very difficult to look at both from 

 the same point of view. Men's minds are preoccupied with the 

 things that they have to do for themselves. The chemistry of 

 the laboratory is seen as a science circumscribed by the labora- 

 tory walls. If it were possible to stand outside, it would be 

 evident that it is only a part of the science of molecular change. 

 Matter changes its state under the influence of force. Many 



