2l8 



CASTELLANl'S ABSORPTION REACTION 



strongly (and which was obtained by immunizing an animal 

 against typhoid) be saturated with typhoid bacilli, centrifugalized, 

 and retested, it will be found that when the serum has lost its 

 power of agglutinating that organism, it will also be bereft of 

 power over the B. coli. On the other hand, if it be saturated 

 with colon bacilli until all its agglutinating power on that 

 organism is removed, its action on B. typhosus will be intact or 

 but slightly reduced. The mechanism by which this is brought 

 about is readily understandable by means of the following diagram 

 (Bolduan). 



Fig. i represents a typhoid bacillus, shown as if it consisted of 

 three varieties of proteid material, A, B, and C, of which A is 

 present in largest amount. The agglutinin formed by its injection 

 will consist of three substances, each specific for its own proteid, 

 and the antibody to A (which we may call the main agglutinin) 



A B C B D E F 



Typhoid Bacillus 



Colon Bacillus 

 E H 



Dysentery Bacillus 



FIG. 45. (After Bolduan.) 



will be most abundant. Fig. 2 represents a colon bacillus, and 

 is shown as consisting of four forms of proteid, of which B is 

 common both to it and to the typhoid bacillus. It follows that 

 the antityphoid serum will clump this bacillus as well as that of 

 typhoid, though not in so high a dilution ; the serum only acts in 

 virtue of its anti-B agglutinin, of which it possesses but a small 

 amount, and this can only act on proteid B, which forms but a 

 small part of the colon bacillus. 



If the serum in question be saturated with typhoid bacilli the 

 whole of the agglutinins are removed in combination with the 

 bacilli, anti-B amongst them, and the serum will become devoid 

 of agglutinating action on both bacilli. 



But if it be saturated with colon bacilli, the only effect will be 

 to withdraw the anti-B agglutinin ; the agglutinins to A and C 

 will remain, and consequently the serum will only lose its clump- 

 ing power on the typhoid bacillus to a slight extent. After 



