V] OF CERTAIN OSMOTIC PHENOMENA 439 



The phenomenon, though a purely physical one, is none too clear. 

 There is a difference of electrical potential between corpuscles and 

 plasma, and the charged corpuscles tend to repel one another; but 

 they also tend to adhere together, all the, more when they meet 

 broadside on, whether by actual stickiness or through surface- 

 energy. The attractive forces then overcome the repulsive, and the 

 rouleau is formed. But if the potential be reduced, and mutual 

 repulsion reduced with it, then the corpuscles stick together just as 

 they happen to meet; rouleaux are no longer formed, and ordinary 

 "agglutination" takes place. Whatever be the precise nature of 

 the phenomenon, the number of rouleaux and the mean number of 



Fig. 146. Sperm-cells of Decapod Crustacea (after Koltzoff). a, Inachus scorpio; 

 b, Galathea sqimmijera; c, do. after maceration, to shew spiral fibrillae. 



corpuscles in each is found, after a given time, to obey a certain 

 law (Smoluchowsky's Law), defining the number of contacts of 

 floating bodies under ordinary physical conditions*. 



The sperm-cells of the Decapod Crustacea exhibit various singular 

 shapes. In the crayfish they are flattened cells with stiff curved 

 processes radiating outwards Hke St Catherine's wheel; in Inachus 

 there are two such circles of stiff processes ; in Galathea we have a 

 still more comphcated form, with long and slightly twisted processes. 



* Smoluohowsky, Ztschr. f. physik. Chemie, xcix, p. 129, 1917; Eric Ponder, 

 On Rouleaux-formation, Q. Journ. Exp. Physiol, xvi, pp. 173-194, 1926. 



