620 SCIENCE PROGRESS. 



the reverse will be true : that by means of a known bacillus 

 we can identify an unknown serum, and can with compara- 

 tive ease ascertain whether an animal is at all, or to what 

 extent, protected. 



That the "agglutinin" is distinct from the bactericidal 

 and paralysing substances in "immune" or other serum 

 appears from the following considerations. An "immune" 

 serum exhibiting strong agglutinative power need not be 

 appreciably more bactericidal than normal serum. A 

 normal serum may exhibit agglutinative without paralys- 

 ing action (7«). Agglutinins are not produced in the 

 serum of animals immunised against certain micro-organ- 

 isms ; e.g., B. diphtheria and certain micrococci. 



Motility of the organism is not, as was at first supposed, 

 essential for agglomeration. Not only can agglutination 

 occur using dead, motionless bacilli instead of active living 

 ones (2/?), but it may be seen also with some non-motile 

 bacteria and cocci. With some cocci I have seen a pheno- 

 menon resembling the loss of movement of motile bacteria. 

 Before the addition of the serum, the cocci usually exhibit 

 a Brownian movement which is much restrained or even 

 entirely inhibited by the action of suitable serum {jb). 



Gruber explains the phenomenon of agglomeration by 

 the supposition that the agglutinin causes the enclosing 

 membranes of the bacilli to swell out and become sticky, 

 and that they consequently adhere to each other when they 

 come in contact. He also put forward the idea that the 

 effect of the special agglutinin is thus to facilitate the action 

 of the general bactericidal substances common to all sera ; 

 and his theory of immunity is based on these two funda- 

 mental ideas. 



The theory has not been unanimously accepted. Pfeiffer 

 considers each serum to have a strictly specific action. 

 Salimbeni does not believe agglutination to occur inside 

 the body (12). Nobody has been able as yet to demon- 

 strate a swelling of the capsule. Be all this as it may, the 

 observed facts, without any theory, form a valuable addition 

 to bacterial knowledge. 



The " active " immunisation of animals is usually attained 



