222 THE H^MAGGLUTININS 



become absolutely fused together into a solid mass, in the centre 

 of which the outlines of the original corpuscles cannot be made 

 out. The macroscopic appearances are similar to those of a 

 Widal's reaction, the emulsion of corpuscles becoming granular 

 and flocculent, and clear rapidly, with the deposition of a red mass 

 at the bottom of the vessel. With a powerful serum a column of 

 emulsion 2 inches high may be completely cleared in five minutes, 

 and the clumping, as observed in a drop of the fluid on a slide, 

 may be complete in a few seconds. 



It will be found that a certain serum does not clump all human 

 corpuscles equally well, and facts have been observed quite 

 comparable to those found by Ehrlich in the case of isohaemo- 

 lysin. According to Landsteiner (whose researches have been 

 corroborated by Hektoen), human bloods may be divided into 

 three groups, which Hektoen describes as follows : 



Group i. Here the corpuscles are not agglutinated by sera of 

 the other groups, whilst the sera agglutinate the corpuscles of 

 both groups. 



Group 2. In this group the corpuscles are agglutinated by the 

 sera of the other groups, whilst the sera agglutinate the 

 corpuscles of Group 3, but not of Group i. 



Group 3. The corpuscles are agglutinated by all other sera, 

 and the sera agglutinate the corpuscles of Group 2, but not of 

 Group i. 



A few specimens of blood are found which do not fit exactly 

 into any of these categories. 



It will be noted that in none of these groups is there an 

 agglutination of red corpuscles by its own serum i.e., an example 

 of the presence of an auto-agglutinin. This substance, however, 

 may occur in the blood, but apparently only in disease. The 

 best example (in fact, the only one in which it has been positively 

 demonstrated) is in pernicious anaemia. In this disease it often 

 happens that the washed corpuscles are immediately and strongly 

 clumped by the serum of the same patient, and the same 

 phenomenon may occur when citrated plasma is used instead of 

 serum. Whether similar phenomena occur in the body, and if 

 not, the reason for its absence, is quite unknown : it is exceedingly 

 difficult to imagine that clumps similar to what we see in vitro 

 can be formed in the circulation, for they appear to be much too 

 large to pass through the capillaries. The only plausible explana- 

 tion is that the auto-agglutinin does not exist as such in the 



