SPECIAL PROPERTIES OF BLOOD SERUM. 2/1 



together in the blood just as the different proteins may exist 

 side by side. 



Through the process of immunization the blood of the ani- 

 mal acquires not only the power of attacking the specific bac- 

 terium, but also the toxins of this bacterium. At least two 

 kinds of anti bodies are therefore produced and there are con- 

 ditions in which only one of these may be active. A serum 

 may be active in the breaking down of bacterial cells, but inert 

 as against the poisons produced by such cells. The complexi- 

 ties of the phenomena, however, cannot be detailed here. It 

 should be said further that bacteria produce hemolysins, which 

 are probably part of the toxins secreted. At any rate some of 

 the toxins found in cultures are strongly hemolytic. 



Agglutinins. Among the several modes of defense ob- 

 served in sera of various animals that of agglutination of in- 

 vading cells must next be briefly considered. We have seen 

 that blood cells and bacterial cells may suffer a kind of dissolu- 

 tion through the action of hemolysins or bacteriolysins, and 

 that a foreign serum is attacked by the precipitins. In addition 

 to these defensive anti bodies there are present others which 

 work by agglutinating or precipitating cells. A certain simil- 

 arity exists between these bodies and the precipitins, but inves- 

 tigations appear to show that they are distinct. The agglutin- 

 ating power is found in normal serum, and like the other anti 

 agencies it may be greatly increased artificially and by the 

 same general means. Agglutinins as precipitating agents en- 

 ter into a loose kind of combination with the cells which they 

 throw down. There is here a suggestion of combination in 

 some kind of chemical proportions. 



Bacteria agglutinins and blood cell agglutinins are to some 

 extent specific, but apparently less so than are the precipitins. 

 Because of this specificity the phenomenon has been applied in 

 a method of diagnosis. Following observations of Gruber 

 and others, Widal suggested a test which is now commonly 

 employed in diagnosis of typhoid fever. It is essentially this : 

 Widal Test. A small amount of the blood or serum of 



