194 Prof. Muir and Mr. Martin. On the Combining [Jan. 18, 



There is, therefore, only a slight difference as regards absorbing powers in 

 favour of the Staphylococcus aureus. 



The immune serum was tested at the same time, and once more a great 

 difference is brought out. 



Immune Serum. 



Opsonic index. 



Anti-staphylococcus serum (heated at 55° C.) 26'7 



„ „ treated twice with B. coli 25'4 



„ „ „ Staphylococcus aureus... 1'6 



These results, as regards the specificity of the normal opsonins, appear to 

 be at variance with the results obtained by Bulloch and Western. They 

 found only a slight reduction of the tubercle opsonin of normal human serum 

 on treatment with the Staphylococcus aureus, and of the staphylococcus 

 opsonin on treatment with the tubercle bacillus. As stated above, we found 

 a great reduction of the staphylococcus opsonin on treating the normal 

 rabbit's serum with the tubercle bacillus. The difference in the results 

 probably depends upon the amount of the bacterial emulsion employed. In 

 every case we used a large amount ; in the tubes after centrifugalisation, the 

 volume of the deposit of bacteria would be about a tenth of the volume of 

 the serum, sometimes more. This is, no doubt, a large quantity, but it is to 

 be noted that the same amounts were employed in the case of the immune 

 serum, and no diminution of the opsonin was observed. The difference in 

 the two kinds of serum is, therefore, very remarkable. 



"We have stated above that the opsonin for a particular organism appears 

 to be more rapidly removed from a normal serum by an emulsion of that 

 organism than of any other, whilst at the same time any bacterial emulsion 

 will absorb large quantities of that opsonin. At present we are unable to 

 give the explanation of that fact. We use the term " normal opsonin " for 

 the labile substance which is destroyed by heat, but we do not know whether 

 or not another substance is present in small amount which acts as an 

 immune body. The problem is very much the same as in the case of 

 bactericidal action. A closely analogous phenomenon was demonstrated by 

 Bordet* in the case of haemolysis. Normal guinea-pig's serum, after treat- 

 ment with rabbit's corpuscles, is deprived of its lytic action for these 

 corpuscles ; it still, however, produces lysis of pigeon's corpuscles. If, 

 however, the serum be treated by a more powerful absorber of complement, 

 viz., rabbit's corpuscles treated with immune-body, it loses also its hemolytic 

 action on pigeon's corpuscles. And it has been shown in our previous paper 

 that an emulsion of a bacterium treated with immune-body absorbs more 

 * Bordet, ' Annates de lTnst. Pasteur,' 1901, p. 317. 



