FUNCTIONS OF LIVING MATTER 7 



simpler materials; and (b) disintegrate e or katabolic changes, in 

 which complex bodies (including the living substance) are broken 

 down into comparatively simple products. In plants, upon the 

 whole, it is integration which predominates; from substances so 

 simple as the carbon dioxide of the air and the nitrates of the soil 

 the plant builds up its carbo-hydrates and its proteins. In animals 

 the main drift of the metabolic current is from the complex to the 

 simple; no animal can construct its own protoplasm from the 

 inorganic materials that lie around it; it must have ready-made 

 protein in its food. But in all plants there is some disintegration; 

 in all animals there is some synthesis. The progress of biochemistry 

 in recent years has indeed shown that the synthetic powers of 

 animal cells have been greatly underestimated. (2) The living sub- 

 stance is excitable that is, it responds to certain external im- 

 pressions, or stimuli, by actions peculiar to each kind of cell. 

 (3) The living substance reproduces itself. All the manifold activities 

 included under these three heads have but one source, the trans- 

 formation of the energy of the food. It is not, however, upon the 

 whole, peculiarities in food, but in molecular structure, that underlie 

 the peculiarities of function of different living cells. A locomotive 

 is fed with coal; a steam-pump is fed with coal. The one carries 

 the mail, and the other keeps a mine from being flooded. Wherein 

 lies the difference of action ? Clearly in the build, the structure of 

 the mechanism, which determines the manner in which energy shall 

 be transformed within it, not in any difference in the source of the 

 energy. So one animal cell, whwi it is stimulated, shortens or con- 

 tracts; another, fed perhaps with the same food, selects certain 

 constituents from the blood or lymph, and passes them through its 

 substance, changing them, it may be, on the way; and a third sets 

 up impulses which, when transmitted to the other two, initiate the 

 contraction or secretion. In the living body the cell is the machine ; 

 the transformation of the energy of the food is the process which 

 ' runs ' it. The structure and arrangement of cells and the steps 

 by which energy is transformed within them sum up the whole of 

 biology. 



PRACTICAL EXERCISES ON CHAPTER I. 

 Reactions of Proteins. 



i. General Reactions of Proteins. Egg-albumin may be taken as a 

 type. Prepare a solution of it by adding water to white of egg, which 

 consists mainly of egg-albumin with a little globulin. In breaking the 

 egg, take care that none of the yolk gets mixed with the white. Snip 

 the white up with scissors in a large capsule, then add ten or fifteen 

 times its volume of distilled water. The solution becomes turbid from 

 the precipitation of traces of globulin, since globulins are insoluble in 

 distilled water. Stir thoroughly, strain through several layers of muslin, 

 and then filter through paper. 



