204 COLLOIDS IN BIOLOGY AND MEDICINE 



Since bacteria, like other proteins, may be precipitated by acids 

 without previous treatment with agglutinating serum, L. MICHAE- 

 LIS and BENIASCH tested different groups of bacteria (typhoid, para- 

 typhoid, colon, etc.) to determine whether the result depended on 

 the H ion concentration. They found that different concentrations 

 of H ions were necessary for the precipitation of different groups of 

 bacteria. The discoverers based on this fact, a method for distin- 

 guishing certain bacterial groups. It is still a question whether the 

 procedure is practical either alone or in combination with agglutinat- 

 ing serum (see S. GALITZER). 



Blood corpuscles, resembling bacteria, behave like a hydrophile 

 suspension whose surface is so changed by various agglutinins that 

 they flock out. I am inclined to believe that a true glueing together 

 occurs more frequently with blood corpuscles than with bacteria. 



From our previous experiments, we see that colloids and suspen- 

 sions are precipitated not only by electrolytes but also by colloids of 

 opposite charge. It must therefore be possible to agglutinate or- 

 ganized suspensions as bacteria and blood corpuscles by suitable 

 hydrosols. Experiments with hydrosols of iron, zirconium, thorium 

 oxid and silicic acid l (W. BILTZ, H. MUCH and C. SIEBERT*, also K. 

 LANDSTEINER and N. JAGIC*, GIRARD-MANGIN and V. HENRI*) con- 

 firm this assumption and show that as with other colloid precipi- 

 tations in salt solutions, an optimum proportion between the two 

 colloids must exist, or no precipitation will occur. 



It should be emphasized that the combination of bacteria or blood 

 corpuscles and inorganic hydrosols is irreversible (in contradistinction 

 to the agglutinin combination). 



Blood corpuscles differ very greatly in one respect from bacteria. 

 Though the latter migrate to the anode showing their negative 

 charge, blood corpuscles are more amphoteric. As a result of this, 

 they are precipitated by negative hydrosols (arsenic tri-sulphid, 

 silicic acid, etc.) L. HiRSHFELD* 2 . A very important observation is 

 that of L. HIRSHFELD, that the agglutination of blood corpuscles of 

 different animals by zinc nitrate follows the same order of precipita- 

 bility as their agglutination by agglutinating sera and abrin. 



Ricin and abrin also agglutinate blood corpuscles, obviously, be- 

 cause they precipitate their albumin. 



From our entire exposition, it is evident, that the adsorption of the 

 agglutinating substance and the agglutination are two separate proc- 

 esses which, in their principle, have nothing in common. The agglu- 

 tinin changes the bacteria or erythrocytes, making them agglutinable; 



1 Colloidal silicic acid agglutinates in much greater dilution than the crys- 

 talloidal. 



