376 STUDIES IN IMMUNITY. 



by horse alexin; one might almost say that it increases their sen- 

 sitivity. We purposely avoid using this expression, since it might 

 lead to a supposition that bovine serum contains a real sensitizer 

 for its own corpuscles. If the term sensitization were loosely used, 

 it might, perhaps, be employed in this case, that is to say, if it were 

 used in the sense of rendering the corpuscles more susceptible to 

 destruction, as is the case when the amount of sodium chloride 

 present is diminished; the word sensitization, however, has been 

 used in a more exact sense by one of us for some time, which suffices 

 to prohibit its use in the present instance as applied to bovine 

 serum. We know, indeed, that the true sensitizers do not affect 

 their proper corpuscles and, on the other hand, that corpuscles that 

 have once been properly sensitized do not need the aid of another 

 sensitizer in order to be hemolyzed by alexin. In a similar way it 

 is evident that this substance in bovine serum should not be con- 

 fused with the ordinary agglutinins, although it does lead to an 

 agglutination. 



We find, in fact, only one logical explanation for this peculiar 

 activity of bovine serum; and in order to elucidate the following 

 discussion we may announce this explanation at once, although it 

 is experimentally proved only in subsequent pages. We believe 

 that there exists in bovine serum a peculiar substance that resists 

 heating to 56 degrees (and, it may be added, is retained in heated 

 serum for months), of an apparently albuminous and colloidal 

 nature, which shows no effect on red blood cells so long as they are 

 under normal conditions, but which unites with them as soon as 

 they are laden with sensitizer and alexin. We have to deal, we 

 believe, with a pure phenomenon of molecular adhesion. From the 

 point of view of properties of molecular adhesion it is evident that 

 normal corpuscles differ from the complex that results in a mixture 

 of corpuscles, sensitizer and alexin, inasmuch as this complex has 

 the property of attracting and binding to it this substance in ox 

 serum that the normal corpuscle does not possess. The adhesion 

 between this substance and sensitized and alexinized corpuscles 

 produces their agglutination in large clumps and also leads to a 

 modification in them which renders them more easily hemolyzed 

 by alexins of moderate potency. 



We shall refer briefly from this time on to this substance in bovine 



