II] THE LEAST OF ORGANISMS 45 



diminishing organism will have greatly changed in all its physical 

 relations, and must at length arrive under conditions which must 

 surely be incompatible with anything such as we understand by 

 life, at least in its full and ordinary development and manifestation. 



We are told, for instance, that the powerful force of surface- 

 tension, or capillarity, begins to act within a range of about 

 1/500,000 of an inch, or say 0-05 ^u,. A soap-film, or a film of oil 

 upon water, may be attenuated to far less magnitudes than this ; 

 the black spots upon a soap-bubble are known, by various con- 

 cordant methods of measurement, to be only about 6 x 10-'^ cm.^ 

 or about -006 /x thick, and Lord Rayleigh and M. Devaux* have 

 obtained films of oil of -002 /x, or even -001 fi in thickness. 



But while it is possible for a fluid film to exist in these almost 

 molecular dimensions, it is certain that, long before we reach 

 them, there must arise new conditions of which we have Uttle 

 knowledge and which it is not easy even to imagine. 



It would seem that, in an organism of -1 /x in diameter, or even 

 rather more, there can be no essential distinction between the 

 interior and the surface layers. No hollow vesicle, I take it, can 

 exist of these dimensions, or at least, if it be possible for it to do 

 so, the contained gas or fluid must be under pressures of a formid- 

 able kindf, and of which we have no knowledge or experience. 

 Nor, I imagine, can there be any real complexity, or heterogeneity, 

 of its fluid or semi-fluid contents ; there can be no vacuoles within 

 such a cell, nor any layers defined within its fluid substance, for 

 something of the nature of a boundary-film is the necessary 

 condition of the existence of such layers. Moreover, the whole 

 organism, provided that it be fluid or semi-fluid, can only be 

 spherical in form. What, then, can we attribute, in the way of 

 properties, to an organism of a size as small as, or smaller than, 

 say -05 [x ? It must, in all probability, be a homogeneous, structure- 

 less sphere, composed of a very small number of albuminoid or 

 other molecules. Its vital properties and functions must be 

 extraordinarily limited ; its specific outward characters, even if we 

 could see it, must be nil ; and its specific properties must be httle 

 more than those of an ion-laden corpuscle, enabhng it to perform 



* Cf. Perrin, Les Atomes, 1914, p. 74. 



t Cf. Tait, On Compression of Air in small 'Bubbles, Proc. B. S. E. V, 1865. 



