1906.] On Opsonins in Relation to Red Blood-cells. 11 



the results obtained do not permit a conception of the nature of the 

 interaction of red cell and opsonin to be formed. 



In a stoichiometric reaction which proceeds slowly, not only is it possible 

 to establish the molecular character of the reaction by means of determina- 

 tions of the reaction rate, but the degree of the reaction may also be 

 ascertained. The general formulas for stoichiometrical reactions are 



t"-t' = HogC7C" 

 for monomolecular reactions, and 



t"-f = ^[l/(C ,, ) B ~l/(C , ) n ] 

 for multimolecular reactions, where C is the concentration at time t' ', C" that 

 at time t", n is unity for bimolecular reactions, and h is a constant. The 

 truth of these formulae has been established for homogeneous systems. 

 Whether they are applicable to heterogeneous systems as in the interaction 

 of toxin and antitoxin has been called in question. In the case of the 

 heterogeneous system formed by red blood-cell + opsonin, the data above 

 given enable the applicability of the formulse in question to be tested 

 empirically. In Table IV, from the data furnished by Table III which are 

 repeated, the values of h are calculated: (1) as for a monomolecular 

 reaction ; (2) f or n = 1 ; and (3) for n = 2.* The values of k for the first 

 and third formulas exhibit wide variations ; the values for n = 1 show a fair 

 correspondence, the average of all the experiments being 0*0014, while the 

 highest and lowest values are 0*0008 and 0*0025 respectively. Thus the 

 striking result is obtained that in the heterogeneous system under considera- 

 tion a relation is exhibited similar to that observed in a bimolecular 

 stoichiometric reaction occurring in a homogeneous system. 



Summary. 

 It has been shown that — 



1. By employing phagocytosis as a test of the presence of red blood-cell 

 opsonin, and avoiding spontaneous phagocytosis by suitable conditions of 

 experiment, quantitative determinations of the opsonic content of serum may 

 be made. 



2. In the experiments made, the interaction of opsonin and red blood-cell 

 proceeded at a rate corresponding to that exhibited in a bimolecular 

 stoichiometric reaction. 



In conclusion, I must express my indebtedness to the assistance I have 

 received from Dr. Allan Macfadyen, in whose laboratory this research was 

 conducted, and from Mr. J. A. Craw and Professor Donnan. 



* The concentrations of red blood-cell and of opsonin are regarded as equivalent, since 

 the opsonin is present in the minimum proportion necessary to lead to full sensibilisation 

 of the red blood-cells. 



