BACTERICIDAL OR ANTI-BACTERIAL IMMUNITY. 191 



substance iii lytic serum, so also the agglutinating substance may be 

 fixed and removed from serum by placing in contact with the serum 

 some of the corpuscles of the particular animal species or some of the 

 bacteria under whose influence the agglutinative substances were formed. 



While. agglutinative substances are developed in the process of im- 

 munization, they are not, so far as we know, directly protective, though 

 by the grouping of micro-organisms the action of phagocytes may be 

 favored. The virulence of pathogenic bacteria is not reduced by agglu- 

 tination. 



The agglutinative seem to differ in many ways from lytic substances. 

 Thus their activities are not suspended by a temperature of 56 C. They 

 become inert, however, at a higher temperature 70 .to 78 C. and 

 their agglutinating capacity is not restored by the addition of normal 

 serum. It is inferred from this fact that the receptors concerned in 

 agglutination are of simpler character than those through which lysis 

 is secured. 



The normal blood serum of some animals contains substances which 

 are agglutinative for the red cells of other species. Thus normal beef 

 serum is agglutinative for the corpuscles of the cat and rabbit. This 

 capacity of the normal serum sometimes is, sometimes is not, associated 

 with marked lytic capacity. 



The mode of action of these so-called agglutiuins is not yet very 

 clearly understood, but a great many interesting facts have been devel- 

 oped in the studies on the general phenomena of agglutination which we 

 cannot mention here. 1 



Precipitating Substances, There is still another way in which the 

 body reveals adaptive alterations in the presence of foreign proteid sub- 

 stances. If a few cubic centimetres of the blood-serum or exudate con- 

 taining globulin from one animal be injected into the subcutaneous tissue 

 or peritoneal cavity of another species in repeated doses, it is found that, 

 on adding a little of the blood-serum of the adapted animal to a dilution 

 of the fluid injected, a precipitate is formed. This reaction is also spe- 

 cific, save that in some instances body fluids from closely related species, 

 such as man and monkey, fowl and pigeon, sheep and goat, horse and 

 ass, dog and fox, may both afford a pecipitate. But this precipitate is 

 invariably much more marked in the fluid used for adaptation than in 

 the similar fluid from the related species. 



This reaction is extremely delicate, it having been possible to recog- 

 nize human blood in a dilution of 1 : 50,000. 



By the use of this test Euttall, who has made very extensive observa- 

 tions, has been able to demonstrate in a most striking fashion phyloge- 

 netic relationships between animal species and groups of species, both 

 warm- and cold-blooded, which have an important bearing upon classi- 

 fication. 2 



The use of this precipitation test has been urged in forensic medicine 



1 For reference to bibliography of Agglutination, see page 237. 

 8 See Nuttall, "Blood Immunity and Blood Relationship," 1904. 



