THE PRESENT POSITION OF CELL-THEORY. 233 



their optical properties and the imbibition of water. But it 

 is a physico-chemical conception, and the molecular aggre- 

 gate need not and should not be endowed with independent 

 vital powers. Such a molecular aggregate is the micella. 

 In accepting the micella one may attribute any amount of 

 complexity to protoplasmic structure without for a moment 

 admitting that it is a cono-eries of elementary organisms. 

 Nor need we admit all the theories which Nageli has tried 

 to establish as the necessary consequences of the assumption 

 that there are such things as combinations of polyatomic 

 molecules into groups of a higher order. As I have already 

 said, it was pointed out by von Sachs that even in the 

 region of pure chemistry it is necessary to assume that polya- 

 tomic molecules are grouped into closer molecular unions, 

 thus giving rise to chemical properties which did not belong- 

 to the individual molecules. But in the region of pure 

 chemistry such a grouping is not called an organisation, 

 nor is there any reason why it should be called an organisa- 

 tion in the present case. Let us be perfectly definite and 

 say that by a micella we mean a combination of polyatomic 

 molecules into closer union to form a group ; nothing more, 

 except in so far as we may reason on chemico-physical 

 grounds as to the behaviour of such groups and their 

 relations inter se. For instance (I am quoting from O. 

 Hertwig's summary of this part of the micellar theory) : 

 "The micellae exert an attraction both on water and on one 

 another, whereby the phenomena of swelling may be ex- 

 explained. In a dry organic body the micellae lie close to 

 one another, separated only by exiguous envelopes of 

 water : these latter enlarge considerably during imbibition, 

 since the attractive forces between the micellae and water 

 are at first greater than between the micellae themselves. 

 The micellae are separated from one another by the imbibed 

 water as it were by a wedge ; but an organised body does not 

 arrive at a condition of solution, since the attraction of the 

 micellae for water diminishes in the course of their separa- 

 tion from one another, at a greater rate than the attraction 

 of the micellae for one another, and therefore, when the 

 watery envelopes have attained a certain size, a condition 



