Acquired immunity against micro-organisms 259 



metchnikovi) develop in the serum of vaccinated animals in the 

 form of elongated filaments more or less interlaced, I was quite 

 prepared to allow that this fact might be of general import. But 

 the study of a cocco-bacillus which produces the pneumo-enteritis of 

 swine and which was isolated by Chantemesse during an epizootic 

 at Gentilly, led me to believe that this was not the case. As this 

 bacillus is characterised by great motility, I concluded 1 that it 

 was identical with that of the hog cholera of American writers. 

 Theobald Smith 2 , to whom I sent a specimen and who is a competent 

 authority on this question, refers it, however, to the species which 

 produces swine plague. Knowing that the question of these two 

 bacteria is not finally settled, it is impossible to come to an absolute 

 decision in the matter. Fortunately, from the point of view of 

 immunity, this is of no great importance. The point upon which 

 I must lay stress is that the serum of rabbits vaccinated against 

 the Gentilly bacillus, when sown with this cocco-bacillus, gave very 

 abundant and uniformly turbid growths. In my researches, under- 

 taken at a period when the rapid agglutination of micro-organisms 

 added directly to the specific serum had not yet been recognised, 

 I noted merely that the cocco-bacilli which grew in the blood serum 

 of vaccinated rabbits presented their normal form and gave rise to 

 a general turbidity of the fluid. Since then, however, it has often 

 been observed that the mode of development of a micro-organism 

 in a serum gives an even more delicate indication than does the 

 agglutination properly so called, produced by the serum to which [273] 

 has been added an organism cultivated on its usual medium. Thus 

 Pfaundler 3 saw that Bacillus coli and Proteus vulgaris, which were 

 not agglutinated by certain serums, developed in them in an unusual 

 fashion and produced very long and interlacing filaments. When 

 a serum is incapable of revealing its properties by agglutinative 

 reaction properly so called, it is sown with the corresponding micro- 

 organism and the development is then compared with that observed 

 in a normal serum. Frequently a very marked difference is noted, 

 the same organism growing into filaments in the specific serum and 

 forming rods only in the normal serum. The first mode of develop- 

 ment is sometimes designated " Pfaundler's reaction." 



1 Ann. de FInst. Pasteur, Paris, 1892, t. vi, p. 289. 



2 Centralbl.f. BakterioL u. Parasitenk., Jena, 1894, Bd. xvi, S. 235. 



8 Centralbl.f. Bakteriol. u. Parasitenk., Jena. I" Abt., 1898, Bd. xxm, SS. 9, 71, 

 131. 



172 



