1906.] On Opsonins in Relation to Red Blood-cells. 5 



amount of serum employed causes any recognisable augmentation of the 



degree of phagocytosis obtainable. From this it may be concluded that, as 



far as phagocytosis is concerned, this ratio represents complete sensibilisa- 



tion. This does not, however, represent the maximum amount of opsonin 



which can be taken up, for it appears, from Table I, that the red blood-cells 



of one part of guinea-pig's blood in some of the experiments removed opsonin 



to such an extent from four parts of serum that the serum was no longer 



capable of sensibilising red blood-cells, though in other experiments sufficient 



opsonin for this purpose was still left. An explanation of the difference in 



the amount of opsonin taken up in the two cases is probably to be found in 



the circumstances that phagocytosis is essentially a surface phenomenon 



depending upon the degree to which the outer part of the red blood-cell is 



sensibilised, and no advantage arises from the opsonin acting upon the cell 



in its whole thickness. 



A striking fact becomes evident from Table II, namely that dilution of 



the serum does not arrest the process of sensibilisation of red blood-cells. 



When the red cells of one part of guinea-pig blood are mixed with oue part 



(or more) of serum, sensibilisation occurs and phagocytosis results equally 



whether the serum is undiluted or is mixed with as much as 500 parts of 



0'85-per-cent. sodium chloride solution. 



/B 1\ 

 The ratio noted above ( ^ = T/ as representing the minimum relative 



amount of serum necessary for the production of marked phagocytosis 

 enables an idea to be formed of the delicacy of the test of deopsination 

 employed in Table I. If the red blood-cells of 0*005 c.c. of the blood of the 

 guinea-pig are mixed with 1 c.c. of deopsinated serum, and are found to 

 become so far sensibilised that marked phagocytosis is obtained, it follows 

 that the serum contains, after deopsination, at least 0*5 per cent, of the amount 

 of opsonin originally present. If, however, phagocytosis is found, on repeated 

 testing, to be always feeble or to be absent, it follows that less than this 

 percentage is present. By adding the red blood-cells of varying amounts 

 of guinea-pig's blood to 1 c.c. of the serum, and noting the point at which 

 sensibilisation becomes incomplete and phagocytosis feeble or absent — and, as 

 is illustrated in Table II, this point is indicated with a fair amount of 

 clearness if a sufficient number of experiments are made, the same technique 

 being closely followed in each — it appeared to be feasible to ascertain 

 approximately the degree to which opsonin had been removed from the serum 

 in question. 



Influenced by this line of thought, the series of determinations in 

 Table III, which forms a continuation of Experiments 8 to 21 in Table I, 



