162 IMMUNOLOGY 



complement occurs early in the reaction before large aggregates 

 are formed and when the optimum surface of sensitized colloid is 

 available for absorption. 



Nonspecific Adsorption. — Cells whose surface contains lipoids 

 seem to be able to adsorb complement in a nonspecific manner. 

 Landsteiner and von Eisler suggest the importance of lipoids in 

 certain nonspecific complement fixations. They conclude, how- 

 ever, that the colloidal state is the important factor in this non- 

 specific fixation. Wilde (1901) noted that emulsions of most 

 bacteria adsorl) complement even when not sensitized. This is im- 

 portant in view of the use of bacterial complement fixation in the 

 diagnosis of certain diseases as well as in the identification of 

 micro-organisms. 



Chemical and Physical Factors in Cell Sensitization. — In 

 other chapters cell sensitization, or the union of antigen and anti- 

 body, is discu.ssed extensively. The phenomenon of specificity 

 which seems to depend upon the chemical constitution of the 

 antigen forces one to recognize definite chemical factors in the 

 process. The evidence seems to bear out Bordet's contention that 

 adsorption plays a prominent part and that the antibody globulin 

 appears to become insoluble in saline. The sensitized cells behave 

 in cataphoretic experiments like particles of denatured globulin. 

 The reaction occurs quite readily at 0° C. Purely chemical re- 

 actions occur very slowly in aqueous systems at low temperatures, 

 but the rate is greatly accelerated as the temperature is increased. 

 Adsorption phenomena, on the other hand, are noticeably increased 

 with the lowering of temperatures, and hence occur readily at 

 0° C. 



At the present time there are two concepts of adsorption that 

 should be borne in mind. Adsorption may be illustrated by the 

 removal of coloring matter from water by means of powdered 

 charcoal. According to one theory, this is accomplished by the 

 molecular capillary state of the surface, while according to an- 

 other concept the valences of the molecules within the charcoal 

 are all satisfied because they are united with each other, but those 

 at the surface have unsatisfied valences or fields which unite with 

 the coloring structure and physical state of the dye as well as the 

 adsorbing surface. It would seem probable that either or both 



