160 THE AGGLUTININS. 



because motility of the individual organisms is greater in the formeF^. 

 and besides the old cultures may contain clumps consisting partly of 

 dead and disintegrated bacterial cells, which may be mistaken fiw 

 typical agglutination. A like source of error is met with when the 

 drop to be examined is allowed to partially dry on the cover-glassi 

 These appearances, which may be mistaken, especially by the inex- 

 perienced, for true agglutination, have been designated pseudo-re- 

 actions. There is also the possibility, especially when dried Uood is 

 used, of mistaking undissolved clumps of red cells, containing thrmds 

 of fibrin for the true clumping of bacilli. 



When exact scientific work is to be done it is better to have the 

 blood drawn directly from a prick on the finger or ear into a gradu?- 

 ated pipette in which the dilution can be made with exactness. 

 There are special tubes made for this purpose, and the pipette which 

 accompanies the ordinary hematocytometer may be used. In hos- 

 pital practice, and especially when a large amount of serum is de- 

 sired, a small Spanish fly blister may be used, and if properly cared 

 for need cause no pain. As has been already stated', cultures killed 

 by heat or those preserved by the addition of formalin, thymol, or 

 some other disinfectant may be used, but these are more or less un- 

 satisfectory, inasmuch as the observer loses the opportunity of 

 watching the gradual decrease of motility. 



As has been stated, Graber and Durham probably expected thai 

 the greatest benefit likely to come from their studies would lie in 

 the &ct that this reaction would furnish a positive means of differ- 

 entiating one species of bacteria fi?om another; It is especially de- 

 sirable that we should have some positive and easily applicable 

 method of distinguishing between the colon and typhoid bacilli, and 

 it was thought that the agglutination test supplies this long-felt want. 

 However, more extended obsecvaiion has shown that typhoid serum 

 occasionally s^gl^tioates the colon bacillus, and very rarely the 

 ag^utination with this oi^ainism may be more marked than i4; i» 

 with the typhoid germ. It may be that in cases of this kind the 

 typhoid patient is suffering from a mixed iofeetion in which both 

 the colon and the ty|^oid bacilli participate. When the agglutina- 

 tion test is used for the purpose of identifying a bacterium the serum 

 used should be taken from an animal immunized to a pure cnltare of 

 that microorganism, and reliance for the differentiation of typhoid 

 and colon bacilli should not be placed in sera obtained from men 

 with typhoid fever. 



It must be plainly evident from what has already been said that 

 the agglutination test has not that specificity which is possessed by 

 the lysins and precipitins. This was plainly seen by Graber and 

 Durham in their original communication, and it has been in- 

 sisted npon by Durham in a later paper, in which he suggests that 

 it would be better to employ the word " »pedal." 



