PHAGOCYTOSIS 273 



Four experiments were carried out, in each of which the fluids 

 (t unit of each) were mixed with i unit of leucocyte "cream," 

 and of a fine emulsion of staphylococci, incubated, and films 

 prepared and counted. Thus : 



Staphylococci in ' , l 

 50 Leucocytes. 



1. Normal serum f normal saline ... ... 170 i'o 



2. ,, ,, + supernatant fluid (b) .. 125 o'6g 

 3- ,, ,, + ,, ,, (a) ... 55 ' 21 

 4. Normal saline + normal saline ... ... 24 



These fluids were then tested in exactly the same way with 

 regard to their action on tubercle bacilli. Thus : 



Tubercle Bacilli T , v 

 in 5 o Leucocytes. 1 



1. Normal serum -f normal saline ... ... 145 i-o 



2. ,, ,, + supernatant fluid (6) ... 132 0-93 

 3- ,, + ,, ,, (V) ... 90 0-6 

 4. Normal saline -[normal saline ... ... 9 



Here it is obvious that the staphylococci have removed the 

 staphylococcic opsonins more powerfully than the tubercle 

 opsonin. The strong emulsion removed 80 per cent, of the 

 former and only 40 per cent, of the latter. 



A striking example of the fact that there is more than one 

 sort of opsonin is supplied by observations on the haemopsonins. 

 Most specimens of blood-serum are unable to act as opsonins 

 for the red corpuscles, which are not taken up by the leucocytes 

 under the ordinary conditions of opsonin investigation in vitro ; 

 but some specimens do possess the power of opsonizing red 

 corpuscles. It is obvious, therefore, that haemopsonin is not the 

 same as bacteriopsonin. 



We must now discuss the nature of these opsonins. Are they 

 familiar substances (e.g., complements or amboceptors) mas- 

 querading under a new name, or are they essentially different ? 

 And if so, are they antibodies, or are they allied to other protective 

 substances, such as the alexins of the cellulo-humoralists or the 

 cytases of Metchnikoff? This is an extremely difficult subject, 

 and one which has not yet been satisfactorily solved. 



The main evidence in favour of the view that they are specific 



1 The indices given are corrected by the deduction of the number of bacteria 

 taken up spontaneously (Expt. 4) from each of the totals. This may be 

 termed the corrected opsonic index, and ought to be given where great 

 accuracy is required. 



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