MECHANLSftl OF ANTIGICN-ANTIBODY REACTIONS 217 



solution to be .studied. The force required to tear the films apart 

 was then determined by a torsion balance." This is illustrated 

 in Fig. 12. 



Extent of Surface Coating. — According to Northrop and 

 DeKruif, it is not necessary for the entire surface of the cells to be 

 coated with agglutinin for clumping to occur. They believe that 

 if an eighth of the area is coated, it will suffice. Shibley found that 

 a])parently tliis is more than is necessary provided tlie other factors 

 arc satisfactory. 



Studies of Bactcrkil Surfaces. — Mudd (1924-1927) and Freund 

 (1925) have made extensive studies attempting to determine the 

 nature of the surface of various types of cells before and after ad- 

 sorption of antibody. The former used the "interfacial tension 

 method" in his investigation and obtained rather significant re- 

 sults. While Mudd and Mudd were primarily interested in the 



Fig. 13. — Interfacial tension technique of Mudd. (After Mudd and Mudd, J. 

 Exper. Med. 43: 148, 1926.) 



phenomenon of opsonification and in phagocytosis, their results 

 definitely support the work of Shibley, Northrop and DeKruif and 

 others in regard to Bordet's phase one Avhere the cells become 

 coated with antibody globulin. 



Interfacial Tension Technique. — This "interfacial tension" 

 technique is described by Mudd and Mudd as follows : 



"A drop of oil is drawn across a carefully cleaned slide. A small 

 drop of dilute blood cell suspeiLsion is drawn along the slide a short 

 distance from and at right angles to the streak of oil. One end of 

 a clean oblong cover slip is touclied to the slide and to the oil so 

 that the oil wets the under surface of the cover slip along one end. 

 The other end of the cover slip is now lowered onto the slide, thus 

 spreading the oil into a film under one side of the slip and the 

 blood into a film adjoining it. In the best preparations the blood 

 film does not cover quite all of the area under its end of the slip." 

 This they also illustrate (Fig. 13). 



