Pleuro- Pneumonia of Cattle. 179 



•question naturally arises : How can the failures to secure posi- 

 tive reactions with the sera from animals which are naturally 

 affected with the disease be explained? It is conceivable, of 

 course, that the amount of antibody (agglutinin) substance pre- 

 sent in the blood serum of a naturally infected animal falls far 

 short of the amount which is produced in an experimental ani- 

 mal as the result of several subcutaneous injections of virulent 

 serosity and culture, and that, while with the latter serum agglu- 

 tination can be observed as a macroscopic reaction, with the 

 serum of a naturally infected animal agglutination may be only 

 partially complete, and may not be recognisable macroscopically, 

 i f it takes place at all. 



An important point which must not be overlooked is the 

 method adopted in the immunisation of Experimental Calf 1. 

 This animal was injected subcutaneously with virulent serosity, 

 and subsequently with virulent serosity, and later with pure 

 -culture in Martin's broth ox serum. 



The serum of an animal immunised in such a manner might 

 possibly contain specific precipitins for ox serum, in which case 

 turbidity in the reaction obtained with the serum of Calf 1, when 

 tested for agglutinins, may have been due to some precipitin 

 element, at least in part. 



Zinsser (1914) (21), in discussing the specificity of precipitins 

 and the precipitin reaction, refers to the experiments of Uhlen- 

 huth, who " obtained a specific anti-hare serum by treating rab- 

 bit's blood with hare's blood — an astonishing result, in view of 

 the close zoological relations between these animals. Isopre- 

 cipitins, that is, precipitins resulting from the treatment of ani- 

 mals with blood from another individual of the same species, 

 have also been described by Schutze and others. They 

 are not, however, regular in their appearance, nor are they very 

 potent when obtained." 11 



It is very improbable, therefore, that an isoprecipitin would 

 be formed in the blood of Calf 1, as a result of the immunising 

 injections of virulent serosity and culture in Martin's broth, 

 each of which injections contained a small amount of ox serum. 

 Even assuming that an isoprecipitin was present, it scarcely seems 

 possible that the serum of Calf 1 could produce by a precipitin 

 reaction alone, such a definite deposit as that which occurred in 

 the agglutination test already referred to. 



11. P. 255. 

 13a 



