46 BENNETT, ON THE MOLECULAR THEORY. 



or mechanical action. They are generally larger in size than 

 histogenetic molecules, are more purely fatty, and, from being 

 associated with the debris of broken-down texture, may, in 

 most instances, readily be distinguished. Thus, in the 

 breaking up of cells and of muscles when they become fatty, 

 or in the putrefaction of vegetable or animal matters, these 

 may be seen to soften, lose their peculiar structure, break 

 up, and ultimately be reduced to a molecular condition. 



We shall subsequently see that these two kinds of mole- 

 cules are constantly changing places, or, in other words, 

 molecular matter formed from the process of disintegration 

 may, Avhen placed under peculiar circumstances, become the 

 basis of matter which undergoes development. In nature, 

 the breaking down of one substance is the necessary step to 

 the formation of another, and the hystolytic or disintegrative 

 molecules of one period become the histogenetic or formative 

 molecules of another. This fact constitutes the basis of the 

 laAv which I shall subsequently seek to establish. 



II. The author pointed out, in the second place, that 

 these molecules are governed by forces, which induce among 

 them a variety of movements, and cause them to combine in 

 definite ways. This force, which we may call molecular 

 force, is altogether independent of cell, nucleus, or other 

 form of structure. 



1st. He alluded to the well-known molecular movements 

 described by Robert Brown. These vibratile, circular, ser- 

 pentine, or irregular motions may be observed whenever 

 molecules are suspended in fluids of certain densities, but 

 are too well known to require notice here. They occur 

 altogether independent of organized structures, and must be 

 regarded as in their nature purely physical. 



2nd. The peculiar movements observed in the interior of 

 cells, vegetable or animal, and during the putrefaction of 

 organic matter. The former are seen in the large vegetable 

 cells of the Cliara, Yallisueria, and Tradescantia, among 

 plants ; and those of chyle, the yolk of the e^g, and of the 

 salivary cell among animals. The author had frequently 

 watched the formation of the latter in putrid fluids. A scum 

 composed of moleciUes collects on the surface; gradually 

 several of these unite in minute filaments more or less long, 

 which assume vibratile or serpentine movements. They are 

 then called vibriones. It has been much disputed whether 

 this class of molecular motions be physical or ^-ital. 



3rd. The movements which are unquestionably vital that 

 occur in the molecules of the yolk, on the entrance into the 

 ovum of the spermatozoid. Here it cannot be maintained 



