PHAGOCYTOSIS 181 



stances? This height may be obtained by setting 8 = 90°, cos = 0, 

 -m/n = 0. Then h 3 = 2, and h = 1.26. The cell has therefore 

 assumed the shape of a hemisphere having a volume equal to the original 

 spherical cell. 



If the nature of the surface G is then changed so that the contact 

 angle = 0, then cos = +1; hence — m/n = +1, i.e., the cell spreads 

 " to infinity." 



If the surface G is such that the cell does not spread at all, then 

 8 = 180° and cos 8 = —1; hence — m/n = — 1. The cell is a free 

 sphere. 



The conclusions are that values of —m/n between +1 and —1 will 

 produce all possible degrees of spreading and that the surface characteris- 

 tics of cell, plasma, and plane determine the magnitude of the contact 

 angle in its equilibrium position. To produce further spreading of the 

 cell, either work must be done on it or the surface characteristics of the 

 interfaces must be changed. 



Phagocytosis 



If a small spherical insoluble particle is substituted for the plane sur- 

 face, comparable changes in the contact area of the cell and particle will 

 take place because of the spreading of the cell over the particle. This 

 factor led Fenn to propose the above analysis as a method of approach in 

 the understanding of the very important biological phenomenon known 

 as phagocytosis. 



Phagocytosis may be defined as the ingestion of a particle by a living 

 cell. The particle may be a non-living piece of matter, a bacterium, or 

 other cell structure. The problem is not to investigate the fate of the 

 ingested particle, but to attempt to analyze the mechanism of phagocyto- 

 sis in terms of the surface energy existing at the interfaces created by the 

 contact of the cell with the particle in the presence of plasma. 



The above theory of cell spreading may be extended to cover cases 

 where the surface G over which the cell spreads is curved to such an 

 extent that G may be considered a small sphere. Under these circum- 

 stances the following questions may arise. What is the physical adjust- 

 ment of the cell, and how does the total surface energy vary as the small 

 spherical particle is progressively ingested? 



It frequently happens in phagocytosis that the cell is about ten times 

 greater in radius than the particle to be ingested, as for instance when a 

 particle in the form of a Staphylococcus aureus of average diameter from 

 0.7 to 1.0 m is about to make contact with a large mononuclear lympho- 

 cyte with average diameter 12 to 15 m- In this example, according to 

 Lyddane and Stuhlman [1940], the above theory shows that the surface 



