454 A NOTE ON ADSORPTION [ch. 



It is found that a rise of temperature greatly reduces the 

 adsorbability of a substance, and this doubtless comes, either in 

 part or whole, from the fact that a rise of temperature is itself a 

 cause of the lowering of surface-tension. We may in all probability 

 ascribe to this fact and to its converse, or at least associate with it, 

 such phenomena as the encystment of unicellular organisms at the 

 approach of winter, or the frequent formation of strong shells or 

 membranous capsules in "winter-eggs." 



Again, since a film or a froth (which is a system of films) can 

 only be maintained by virtue of a certain viscosity or rigidity of 

 the liquid, it may be quickly caused to disappear by the presence 

 in its neighbourhood of some substance capable of materially 

 reducing the . surface-tension ; for this substance, being adsorbed, 

 may displace from the surface -layer a material to which was due 

 the rigidity of the film. In this way a "bathytonic" substance, 

 such as ether, causes most foams to subside, and the pouring oil on 

 troubled waters not only calms the waves but still more quickly 

 dissipates the foam of the breakers. In a very different order of 

 things, the breaking up of an alveolar network, as at a certain stage 

 in the nuclear division of the cell, may be due in part to just such 

 a cause, as well as to the direct lowering of surface-tension by 

 electrical agency. 



Our last illustration has led us back to the subject of a previous 

 chapter, namely to the visible configuration of the interior of the 

 cell, in so far (at least) as it represents a "dispersed system," coarse 

 enough to be visible; and in connection with this wide subject there 

 are many phenomena on which light is apparently thrown by our 

 knowledge of adsorption, of which we took Httle or no account in 

 our former discussion. One of these phenomena is nothing less than 

 that visible or concrete "polarity," which we have seen to be in 

 some way associated with a dynamical polarity of the cell. 



This morphological polarity may be of a very simple kind, as 

 when it is manifested, in an epithelial cell, by the outward shape of 

 the elongated or columnar cell itself, by the essential difference 

 between its free surface and its attached base, or by the presence 

 in the neighbourhood of the former of mucus or other products of 

 the cell's activity. But in, a great many cases, this polarised 

 symmetry is supplemented by the presence of various fibrillae, or 



