TESTING OF PROPERTIES OF SERUM 109 



some wax moulded round its middle, the hair end is slipped 

 through the broken-off end just mentioned, and the tube is fixed 

 in position as shown in the figure. A rubber nipple placed on 

 the end of the pipette completes the apparatus. If by pressing 

 the nipple the air be expelled from the pipette and the end 

 dipped under mercury, exactly 5 c.mm. will be taken up. Thus 

 when pressure on the nipple is relaxed, 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 

 described in connection with agglutination is very useful 

 (see Fig. 46 d). 



The Testing of Agglutinative and Sedimenting Properties 

 of Serum. 



By agglutination is meant the aggregation into clumps of 

 uniformly disposed bacteria in a fluid ; by sedimentation 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 discussed later. Here we shall only give the 

 technique by which the presence or absence of the property may 

 be tested. There are 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 ; sediment- 

 ation is shown by the formation within a given time (say 12 or 

 24 hours) 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 (6) the 

 serum to be tested should never be brought in the undiluted 



