122 GENERAL PHYSIOLOGY 



sulphur be melted in a vessel and the melted mass be poured 

 into water, there is obtained a tough, brown, gummy substance 

 which has not the least external resemblance to the piece of 

 sulphur from which it came. But if it be left for a day or two, 

 it becomes gradually harder and more solid, its brown colour fades 

 and changes to a yellowish, and after some time the whole mass 

 takes on again the appearance of common hard yellow sulphur. 

 Here the sulphur has gone through a development which has 

 made it again like the piece from which it was derived. But 

 even on the part of organisms development is not an absolute sign 

 of difference, for there are organisms that live without developing. 

 The two equal parts into which Amoeba constricts itself are 

 complete Amcubce, without any further process, and are dis- 

 tinguished by their size only from the individual from which they 

 are derived. 



Finally, an endeavour has been made, but with similar slight 

 success, to find a distinction between organisms and inorganic 

 substances in the manner of growth. The unfortunate contrast 

 of the organism and the crystal, again, has led to the assertion of 

 this difference. It has been said that the crystal grows by the 

 apposition, the organism by the intussusception of particles ; i.e., 

 the crystal grows by laying one particle after another upon its 

 surface, the interior remaining fixed and unchanged, the organism, 

 on the contrary, by taking particles into its interior and storing 

 them between those already present. If a cell as a whole be con- 

 trasted with a crystal, this is not to be disputed ; but it has 

 already been seen that as regards its physical characteristics the 

 living substance of organisms in its essentials ought to be com- 

 pared with a liquid. Liquids, however, grow solely by intussus- 

 ception, i.e., if a soluble body be added to a liquid, e.g., salt to 

 water, the latter dissolves the former and stores the molecules of 

 the soluble body by diffusion between its own molecules that is, 

 there is here exactly the same process as in the growth of the 

 organism. 



Hence, the comparison of the genetic relations of organisms and 

 inorganic bodies reveals no more fundamental difference between 

 them than the consideration of their structural relations, and it is 

 necessary to search further. 



3. Physical Differences 



A third group of differences which have been asserted to exist 

 between organisms and inorganic bodies comprises the phenomena 

 of movement. Movement, the most evident of all vital phenomena, 

 was regarded in early times as a characteristic sign of life, and 

 primitive people, in holding consistently to this idea, regarded 

 winds and waves as living things. But the sea is no longer 



