•148 ANTIGENS AND THE TECH NIC OF SERUM REACTIONS 
cerned. First there is loss of motility— "immobilization"— and 
eventually clumping of the immobilized organisms. In general, it 
is not known whether immobilization and clumping are independent 
processes, or successive steps in the same process. Agglutination does 
not of itself kill the organisms. Smith and Reagh^ working with 
non-motile and motile hog cholera bacilli have demonstrated both 
flagellar and somatic agglutinins, the former paralyzing the activity 
of the flagella, the latter agglomerating the orranisms themselves. 
Non-motile bacteria usually agglutinate somewhat more slowly than 
motile organisms. Small amounts of neutral salts are necessary for 
the clumping of bacteria,^ although a union of the specif c organism 
and its agglutinin will take place even if salts are absent. The specific 
substance (or substances) of the bacterial cell which reacts with the 
specific antibody of the serum (agglutinin) is known as agglutinogen. 
Closely related bacteria, as typhoid and paratyphoid bacilli, may 
possess a certain amount of agglutinogen in common, but, as a rule, 
the specific organisms are clumped in immune sera at much greater 
dilution than related organisms are clumped. Also, the specific 
organisms will remove the agglutinin completely from immune sera, 
while closely related bacteria only remove that portion of the agglu- 
tinating substance which is common to both organisms, leaving 
behind the specific agglutinin which will then agglutinate the specific 
organism, but not its closely related fellow; that is to say, closely 
related bacteria will react with the common or group agglutinin, but 
fail to absorb the specific agglutinin. (See Castellani.'') 
Experience has shown that the sera of normal adults frequently 
contain agglutinin which will clump various bacteria and the potency 
of these "normal" or natural agglutinins may even be sufficient to 
clump moderate numbers of typhoid bacilli in dilutions as great as 
1 to 30. The sera of normal nurslings contain only minimal amounts 
of normal agglutinins as a rule, and the conclusion has been drawn 
that normal agglutinin may be either: 
(a) Group agglutinin, derived from mild infection with closely 
related organisms, or 
(&) True immune agglutinins resulting from mild or unrecognized 
infection with the specific organism. 
No definite distinction has been noted between natural and immune 
agglutinins; the latter are usually present in sera, however, in much 
greater concentration than the former. 
The site of formation of agglutinins in the body is not definitely 
known, although lymphoid tissues appear to be intimately concerned, 
especially bone-marrow and the spleen. Pryzgode"* states that 
cultures of spleen tissue in titro will form specific agglutinins for 
1 Jour. Med. Res., 1903, 10, 89. 
2 Bordet: Collected Studies in Immunity, 1909 (translation by Gay). 
3 Ztschr. f. Hyg., 1902, 40, 1. 
4 Wien. klin. W'chnschr., 1913, 26, 841. 
