272 THE FORMS OF CELLS [ch. 



In the second place, it can be exactly imitated artificially by 

 means of other colloid substances. Many years ago Norris made the 

 very interesting observation that in an emulsion of glue the drops 

 assumed a biconcave form resembling that of the mammalian cor- 

 puscles*. The glue was impure, and doubtless contained lecithin ; 

 and it is possible (as Professor Waymouth Reid tells me) to make 

 a similar emulsion with cerebrosides and cholesterin oleate, in 

 which the same conformation of the drops or particles is beautifully 

 shewn. Now such cholesterin bodies have an important place 

 among those in which Lehmann and others have shewn and studied 

 the formation of fluid crystals, that is to say of bodies in which 

 the forces of crystallisation and the forces of surface tension are 

 battling with one another f ; and, for want of a better explanation, 

 we may in the meanwhile suggest that some such cause is at the 

 bottom of the conformation the explanation of which presents so 

 many difficulties. But we must not, perhaps, pass from this 

 subject without adding that the case is a difficult and complex 

 one from the physiological point of view. For the surface of a 

 blood-corpuscle consists of a "semi-permeable membrane,"' through 

 which certain substances pass freely and not others (for the most 

 part anions and not cations), and it may be, accordingly, that we 

 have in life a continual state of osmotic inequilibrium, of negative 

 osmotic tension within, to which comparatively simple cause the 

 imperfect distension of the corpuscle may be also due J. The whole 

 phenomenon would be comparatively easy to understand if we 

 might postulate a stifEer peripheral region to the corpuscle, in the 

 form for instance of a peripheral elastic ring. Such an annular 

 thickening or stiffening, like the " collapse-rings '' which an engineer 

 inserts in a boiler, has been actually asserted to exist, but its 

 presence is not authenticated. 



But it is not at all improbable that we have still much to 

 learn about the phenomena of osmosis itself, as manifested in the 

 case of m^ute bodies such as a blood-corpuscle ; and (as Professor 

 Peddie suggests to me) it is by no means impossible that curvature 



* Prnc B y. Soc. xii, pp. 251-257, 1862-3. 



t Cf. (int. al.) Lehmann, Ueber scheinbar lebende KristaUe und Myelinformen, 

 Arch. f. Enho. Mech. xxvi, p. 483, 1908; Ann. d. Physik, xliv, p 969, 1914. 



f Cf. B. Moore and H. C. Roaf, On the Osmotic Equilibrium of the Red 

 Blood Corpuscle, BiocJiem. Journal, in, p. 55, 1908. 



