384 THE FORMS OF CELLS [ch. 



capable of realisation under surface-tension, and many of them 

 doubtless to be recognised among organisms, which we cannot 

 deal with in this elementary account. The subject is a very 

 general one; it is, in its essence, more mathematical than physical; 

 it is part of the mathematics of surfaces, and only comes into relation 

 with surface-tension because this physical phenomenon illustrates 

 and exemplifies, in a concrete way, the simple an4 symmetrical 

 conditions with which the mathematical theory is capable of deahng. 

 And before we pass to illustrate the physical phenomena by biological 

 examples, we must repeat that the simple physical conditions which 

 we presuppose will never be wholly realised in the organic cell. 

 Its substance will never be a perfect fluid, and hence equilibrium 

 will be slowly reached; its surface will seldom be perfectly homo- 

 geneous, and therefore equilibrium will seldom be perfectly attained ; 

 it will very often, or generally, be the seat of other forces, symmetrical 

 or unsymmetrical ; and all these causes will more or less perturb the 

 surface-tension effects*. But we shall find that, on the whole, these 

 effects of surface-tension though modified are not obliterated nor 

 even masked; and accordingly the phenomena to which I have 

 devoted the foregoing pages will be found manifestly recurring and 

 repeating themselves among the phenomena of the organic cell. 



In a spider's web we find exemplified several of the principles of 

 surface-tension which we have now explained. The thread is spun 

 out of a glandular secretion which issues from the spider's body as 

 a semi-fluid cyHnder, the force of expulsion giving it its length and 

 that' of surface-tension giving it its circular section. It is too viscid, 

 and too soon hardened on exposure to the air, to break up into drops 

 or spherules ; but it is otherwise with another sticky secretion which, 

 coming from another gland, is simultaneously poured over the 



* That "every particular that worketh any effect is a thing compounded more 

 or less of diverse single natures, more manifest and more obscure" is a point made 

 and dwelt on by Bacon. Of the same principle a great astronomer speaks as 

 follows: "It is one of the fundamental characteristics of natural science that we 

 never get beyond an approximation. . .Nature never offers us simple and undivided 

 phenomena to observe, but always infinitely complex compounds of many different 

 phenomena. Each single phenomenon can be described mathematically in terms 

 of the accepted fundamental laws of Nature : . . . but we can never be sure that we 

 have carried the analysis to its full exhaustion, and have isolated one single simple 

 phenomenon." W. de Sitter, in Nature, Jan. 21, 1928, p. 99. 



