232 SCIENCE PROGRESS. 



which they exhibit depend. In fact they describe essenti- 

 ally similar functions in biophors and in cells, but they 

 allow a physico-chemical explanation in one case and 

 disallow it in the other. This contradiction has been 

 noticed by others, and it has never been satisfactorily 

 explained away. Whitman draws attention to it, and 

 observes that no one, as far as he knows, has looked upon 

 the unit as anything more than the seat of the mystery. 

 This is true, but it is no reason for putting" the mystery in 

 a small bag instead of a big one. He defends the theories 

 of smaller units, however, by saying that they have ex- 

 tended our knowledge of organic mechanism {Joe. cit., 

 prefatory note, p. vi.). This again I believe to be true, 

 but not quite in the sense in which Whitman apparently 

 means it to be. The theories of minute independent vital 

 units have, I believe, led many on the wrong track as 

 regards vital mechanism ; the attacks on such theories are 

 leading to a considerable extension of our knowledge in 

 this direction. The ultimate vital units confessedly do not 

 remove the mystery ; ultimately the explanation of life 

 must be a chemico-physical one ; there is no alternative 

 but a vitalistic theory, and this is not admissible in science. 

 The strongest ground, viz., the granular hypothesis, for 

 assuming the presence of vital units is removed by the 

 observed constitution of hyaline protoplasm, and finally 

 none of the assumed aggregates of units which are admitted 

 to be visible, are identified with various sorts of granules 

 and considered to constitute units of a higher order, have 

 ever been shown to be capable of leading an independent 

 existence. 



On the other hand there is a oeneral consensus of 

 opinion that protoplasm is not a simple organic compound. 

 Its unit is not the molecule, but an aggregate of molecules 

 forming a unit of a higher order to which the molecule 

 stands in the same relation as the atom does to the mole- 

 cule. It is also admitted that these molecular aggregates 

 may exist in many different kinds in protoplasm. Such a 

 conception is absolutely necessary for the explanation of 

 the most simple properties of organic bodies, for example, 



