GERMINAL VARIATIONS ARE QUANTITATIVE 63 



tained, as Francis Galton has shown, during long periods of 

 time. 



It may be asked, What, then, is the precise nature of the 

 changes which operate in the germ-plasm ? In ultimate instance, 

 aU such changes are quantitative in their nature. The isomeric 

 combinations known to chemical science are in reality likewise 

 quantitative in the last resort, although apparently qualitative. 

 All changes brought about in the germ-plasm are produced by 

 variations which take place, either in the number of the different 

 elements which go to make up a given combination, or in the 

 arrangement of the elements in a given space. A quaUtative 

 variation of a given determinate can be the result of a variation 

 in the proportion of the elements which go to make up its deter- 

 minants — ^for instance, when the proportion of an element X 

 to another element Y is changed in such a way that the char- 

 acter of the determinate XY^ is thereby altered. Or such 

 quaHtative variation may result from a simple change in the 

 arrangement of its component elements, their number and pro- 

 portion remaining the same, as in the case, for instance, of a 

 beetle on whose back 100 hairs are scattered sparsely, and 

 separated by a certain distance from each other, and whose 

 progeny, when they attain to the condition of adult insects, have 

 the same 100 hairs, but all on one spot, forming a sort of brush. 

 Between the mother beetle and the next generation there is an 

 apparently quaHtative difference — namely, the brush — but this 

 apparently quaUtative difference has simply resulted from a 

 different arrangement of the same number of elements, and is 

 in reaHty a quantitative difference. All differences in the ulti- 

 mate instance are quantitative. Yet there is a sense in which 

 we may fairly say that, through the perturbation of intrager- 

 minal nutrition, each elementary vital element is capable, not 

 merely of quantitative growth or diminution, but also of being, 

 through these nutritional variations, affected qualitatively. 



The nature of the forces which regulate the movements in the 



