METHODS OF TESTING FOR AGGLUTINATION 119 



B 



D 



-E 



when pressure on the nipple is relaxed. Thus other tubes can be 

 very readily calibrated by the mercury being expelled into them, 

 and its limits marked on their bores. 



For measuring equal parts of different fluids, the pipette 

 shown in Fig. 44, d, in connection with 

 agglutination is very useful. 



Methods of testing for Simple Ag- 

 glutination. By agglutination is meant 

 the aggregation into clumps of uniformly 

 disposed bacteria in a fluid ; by sedimenta- 

 tion the formation of a deposit composed 

 of such clumps when the fluid is allowed 

 to stand. Sedimentation is thus the 

 naked-eye evidence of agglutination. The 

 blood serum may acquire this clumping 

 power towards a particular organism under 

 certain conditions, these being chiefly met 

 with when the individual is suffering from 

 the disease produced by the organism, or 

 has recovered from it, or when a certain 

 degree of immunity has been produced 

 artificially by injections of the organism. 

 The nature of this property will be dis- 

 cussed later. Here we shall only give the 

 technique by which the presence or absence 

 of the property may be tested. There are FlG 

 two chief methods, a microscopic and a 

 naked-eye, corresponding to the effects 

 mentioned above. In both, the essential 

 process is the bringing of the diluted 

 serum into contact with the bacteria 

 uniformly disposed in a fluid. In the 



former this is done on a glass slide, and the result is watched 

 under the microscope the occurrence of the phenomenon is 

 shown by the aggregation of the bacteria into clumps, and if the 

 organism is motile this change is preceded or accompanied by 

 more or less complete loss of motility. In the latter method 

 the mixture is placed in an upright thin glass tube ; sedimenta- 

 tion is shown by the formation within a given time (say from two 

 hours at 37 C. to twenty- four hours at room temperature) of a 

 somewhat flocculent layer at the bottom, the fluid above being 

 clear. Two points should be attended to : (a) controls should 

 always be made with normal serum, and (b) the serum to be 

 tested should never be brought in the undiluted condition into 



C 



F 



m A 5 



casing of ^m tiibing; 

 B, rubber nipple ; C, 



c.mm. capacity ; D to 

 E > nair capillary. 



