178 STUDIES IN IMMUNITY. 



a perfectioning of, or an increase in, preexisting properties, and it 

 is therefore of interest to ascertain whether the active substances 

 in the sera of vaccinated animals have characters in common with 

 similar substances in normal sera and whether, indeed, the two are 

 identical. For example, we may compare the antihematic proper- 

 ties which are so strongly marked in the serum of animals treated 

 with defibrinated blood with similar properties present in normal 

 sera. 



The property of agglutinating and dissolving alien red blood 

 cells is found very commonly in normal sera. We know that these 

 properties affect the corpuscles from different animal species only. 

 Following is a recapitulation of the agglutinating power of certain 

 normal sera on certain varieties of red blood cells. In these experi- 

 ments we usually mixed one part of defibrinated blood with three 

 or four parts of serum : 



Guinea-pig serum agglutinates the corpuscles of the rabbit and 

 the hen slightly and rat corpuscles more energetically. 



Rabbit serum has slight agglutinating properties for the red 

 blood corpuscles of the guinea-pig, man, the hen and the rat. 



Hen serum has an energetic agglutinating property for the cor- 

 puscles of the dog and rat and especially for the rabbit. Its agglu- 

 tinating action on guinea-pig corpuscles is slight. It agglutinates 

 pigeon corpuscles rather strongly. 



Pigeon serum has a very weak agglutinating property for the 

 corpuscles of the hen, the rabbit, man, and also for bacteria. 



Dog serum agglutinates the corpuscles of the rabbit and the 

 rat strongly, and the corpuscles of the guinea-pig and the hen 

 faintly. 



Rat serum agglutinates the corpuscles of the rabbit and the 

 guinea-pig slightly. 



Goat serum agglutinates the corpuscles of the rabbit and the 

 guinea-pig distinctly. 



Horse serum agglutinates the corpuscles of the guinea-pig, the 

 rabbit and the hen distinctly and the corpuscles of the rat ener- 

 getically. 



The dissolving properties of these animal sera for red blood 

 corpuscles are always due to the alexin, or thermolabile sub- 

 stance. It is a general rule, applicable to all sera, that the 



