98 THE PRINCIPLES OF IMMUNOLOGY 



Space does not permit a complete discussion of the results of the 

 test, but it may be said that a positive Dreyer test indicates the 

 presence of some form of enteric fever. If, however, the isolation 

 of organisms from the stools indicates the nature of the disease the 

 test may sometimes mislead. For example, we have found para- 

 typhosus B in the stools of a patient whose serum titer curve indi- 

 cated the presence of a para A infection. The test should go hand 

 in hand with careful clinical study and bacteriological examination 

 of the blood, feces, and urine. 



Hemagglutinins. The agglutination of blood-cells and other 

 body cells follows the same general principles laid down for bacterial 

 agglutinins. In the case of agglutinins for red blood-corpuscles the 

 name hemagglutinins has been adopted. These may be divided into 

 auto-hemagglutinins, iso-hemagglutinins, and hetero-hemagglu- 

 tinins. The auto-hemagglutinin is contained in the same blood as 

 the cells it agglutinates, but certain factors operate to prevent agglu- 

 tination in the living body. For example, Rous and Robertson have 

 shown the presence in rabbits, which had received repeated small 

 blood transfusions, of an auto-hemagglutinin which operates at 

 temperatures lower than that of the animal, but on raising the tem- 

 perature to 38 to 40 C. the clumps break up and a homogeneous emul- 

 sion results. The same workers also demonstrated the presence of 

 auto-agglutinins in rabbits subjected to repeated withdrawal of 

 small quantities of blood. It has been stated that this phenomenon 

 may also occur in acquired hemolytic jaundice (Hayem-Widal 

 type), pernicious anemia, malaria, and other diseases, but more 

 recent studies tend to contradict this statement. Hornby states 

 that auto-hemagglutinins have been demonstrated frequently in 

 animals infected with trypanosomes. Hetero-agglutinins were dis- 

 covered by Creite and Landois, who noted that the serum of certain 

 animals produced agglutination when brought in contact with the 

 cells of certain other species; for example, the serum of the goat 

 and the erythrocytes of rabbit, man, or pigeon. Bordet discovered 

 in the course of his studies on hemolysins that if an animal is im- 

 munized with the erythrocytes of another species, the blood serum 

 will contain not only hemolysin, but also hemagglutinin for the 

 cells used in immunization. Thus we have to consider normal 

 hetero-hemagglutinins and immune hetero-hemagglutinins. Such 

 normal antibodies are present in low titer, but immune agglutinins 

 of this sort may be induced up to titers of several thousand. The 

 methods employed for the production of such agglutinins are the 

 same as those for producing hemolysis and will be considered under 

 that subject. The determination of the titer of hemagglutinative 

 sera is by essentially the same methods as for bacterial agglutinins, 

 save that the cells are washed as for experiments in hemolysis,, and 

 usually a fixed percentage emulsion of cells is employed. The influ- 

 ence of heat and other physical agents, as well as chemicals, is much 

 the same as for hemolysins (see page 115). 



