XVI PRESIDENTIAL ADDKESS 



action of the oxygen of the air this fuel is oxidised or burnt up ; 

 the mechanism consequently does work ; complex chemical 

 changes take place ; and the ultimate resultant is life, manifested 

 by the essentially vital phenomena of movement, irritability) 

 metabolism, or the power of converting the altered nutrient 

 material into its own likeness and reproduction. The pheno- 

 mena of movemement and irritability can be exhibited by that 

 part of the mechani.^m which we still called protoplasm, even if 

 it is deprived of the nucleus, but metabolism and reproduction 

 are essentially functions of the nucleus — that wonderful machine 

 within a machine — which not only insures the continuance of 

 life in the unit itself by enabling it to assimilate and grow, but' 

 which, by the agency of its marvellous constituent, chromatin, 

 is the source of the bewildering problems of heredity. Besides 

 its momentous and, at present, inscrutable resultant — life or 

 vitality — the working of the cell creates a laboratory of the most 

 intricate chemical changes, and gives rise to by-products of such 

 vast importance that without them the whole range of plant life, 

 and consequently of animal life, would be at an end. For 

 instance, in the filaments of spirogyra we saw a spiral band, 

 which is made up of beautiful light green granules, and each 

 cell in the volvox displays the same green substance. This 

 product of cell activity, known as chlorophyll, is the source of 

 green colouring of plants, and is the agent by which, under the 

 influence of sunlight, they are enabled to assimilate carbon 

 direct from the air by decomposing the carbonic acid gas present 

 in it. Without chlorophyll plant life could not exist, and 

 without plant life animal life would cease. There is another 

 product of cell action which is scarcely less important. If we 

 cut a thin section of potato and examine it under the microscope, 

 we find the cells of which it is composed filled with minute 

 grains, which, if carefully focussed, exhibit a fine, scarcely 

 perceptible lamination. If we have a polarizing apparatus on 

 our instrument, and observe these granules under polarised 

 light, each becomes marked with a dark cross. Thi? phenomenon 

 tells us that we are looking at the starch granules which 

 give the potato its flowery quality and nutrient properties. 

 The cell, then, according to the most recent theory, is an intri- 

 cate piece of mechanism — a life-engine — whose parts are admi- 

 rably adapted to the production of vitality. If it is asked 

 whether this theory brings us any nearer to answering the 

 question, " What is life ? " the answer must not only be in the 

 negative, but it must be at once admitted that we are further 



