THE PHENOMENON OF AGGLUTINATION 227 



larly by Kraus and Joachim 27 and by Scheller. 28 Scheller sum- 

 marizes the results of his work as follows : First, in agreement with 

 Joos he found that immune sera obtained by injection of bacteria 

 modified by heat vary considerably from each other. Secondly, im- 

 munization with living typhoid bacilli produces sera which agglu- 

 tinate living bacilli very highly and less highly bacilli heated to 60 

 C. The titre of agglutinating serum is altered very little toward 

 living bacilli after heating to 60 to 62 C., but is sometimes dimin- 

 ished toward bacteria that have been heated. Bacilli that have been 

 heated to 100 C. but slightly agglutinate unheated serum. Sera 

 produced by the injection of typhoid bacilli heated to 60 to 62 C. 

 agglutinate with both living and heated bacilli. Very important 

 furthermore in Scheller's work are the determinations that typhoid 

 bacilli which have been heated absorb agglutinins out of the sera 

 more actively than do the unheated bacteria, and that the highest 

 agglutinin titres can be obtained by agglutination with bacilli that 

 have been heated to 60 C. The analogy of Scheller's results with 

 similar work done in connection with the precipitin reaction is strik- 

 ing and will be referred to in another place. 



Alterations in the agglutinability of bacteria may also occur spon- 

 taneously, without previous heating, as in the preceding experiments. 

 It has been frequently noticed that typhoid bacilli, recently culti- 

 vated out of the human body, will not agglutinate in sera which have 

 high agglutinating power for strains kept for some time on labora- 

 tory media. Much investigation has been focused upon the deter- 

 mination of the cause for this, and although many explanations have 

 been suggested no satisfactory solution has been found. Most work- 

 ers who have attempted to attack this problem have based their rea- 

 soning upon the receptor conception of Ehrlich and have assumed 

 that such inagglutinable bacteria are characterized by a diminished 

 equipment in "receptors." Such strains have been especially well 

 studied in the case of typhoid bacilli and cholera spirilla. Inagglu- 

 tinable typhoid bacilli have been cultivated by many investigators 

 from the spleen, gall bladder, and urine of typhoid patients, and 

 many of these, when studied for prolonged periods, have been found 

 to regain normal agglutinability after several generations of culti- 

 vation upon artificial media. Apparently some alteration of the 

 bacilli had taken place in the presence of the body fluids (immune 

 serum) which affected their sensitiveness to the agglutinins, i. e.,, 

 their ability to unite with or absorb this antibody. The phenomenon 

 involves an important principle, emphasized some years ago by Pro- 

 fessor Welch, namely, that the bacteria may acquire a quasi- 

 immunity against the attacking forces of the body, a property which 

 may be responsible for the increase of virulence noted when some 



27 Kraus and Joachim. Centralbl f. Bakt., I, Vol. 36, 1904. 



28 Scheller. Centralbl /. Bakt., Vol. 36, 1904, and Vol. 38, 1905. 



