1897J MICROSCOPICAL JOURNAL 137 



should have a faint reddish ting-e. The cover-g"lass, with 

 the mixture on the surface, is inverted over a hollow slide 

 (the edges about the concavity having- been smeared with 

 oil or fluid vaseline so as to make a closed chamber), and 

 the hang-ing- drop then examined under the microscope 

 (preferably by g-as lig"ht), a hig-h-power dry lens (about 1-C) 

 inch) beiugf used. 



If thereaction takes placerapidly, thefirst g-lance throug-h 

 the microscope reveals the completed reaction, all the ba- 

 cilli being- in loose clumps and nearly or altogether motion- 

 less. Between the clumps are clear spaces containing- few 

 or no isolated bacilli. 



If the reaction is a little less complete, a few bacilli mav 

 be found moving- slowly between the clumps, in an aimless 

 way, while others attached to the clumps by one end are 

 apparently trying- to pull away, much as a fly caug-ht on a 

 fly-paper strug-g-les for freedom. 



If the ag-g-lutinating- substances are still less abundant, 

 the reaction may be watched throug-h the whole course of 

 its development. Immediately after mixing- the blood and 

 culture tog-ether it will be noticed that manv of the bacilli 

 move more slowly than before the addition of the serum. 

 Some of these soon cease all prog-ressive movement and it 

 will be seen that they are g-athering together in small 

 groups of two or more, the individual bacilli being still somt- 

 what separated from each other. Gradually they close up 

 the spaces between them and clumps are formed. Accord- 

 ing to the completness of the reaction, either all the bacilli 

 may finally become clumped and immobilized or only a 

 small portion of them, the rest remaining freelv motile, 

 and even those clumped may appear to be struggling for 

 freedom. With blood containing a large amount of the 

 agglutinating substances all gradations in the intensity of 

 the reaction may be observed, from those shown in a 

 marked and immediate reaction to those appearing in a late 

 and indefinite one, by simply varying the proportion of 

 blood added to the culture fluid. 



Pseudo Re-actions With Dried Blood. If too con- 

 centrated a solution of dried blood from a health v j'crson 



