TYPHOID FEVER 



79 



f^Hii^^b 



Compare the control-tube with the pipette to which blood has 

 been added. If the reaction is negative, the appearances will be 

 exactly the same in each ; but if the reaction is positive, the bacilli 

 will fall to the bottom in flocculent 

 granular masses, which are similar 

 whether living or dead bacilli have 

 been used. In the former case there 

 is no difficulty in determining whether 

 the reaction is present or absent, for 

 the fluid will be clear if it is positive, 

 turbid if it is negative (Fig. 25). The 

 dead emulsion presents more diffi- 

 culties ; you have to compare the 

 granular deposit which occurs in a 

 positive reaction with the more uniform 

 deposit which occurs in the control- 

 tube. If there is any doubt, the best 

 plan is to break off the tip of the pipette 

 and blow out some of the deposit ; 

 examine it under the microscope after 

 applying a cover-glass. In a positive 

 case the bacilli will be seen to be col- 

 lected into clumps; in a negative case 

 they will remain discrete. 



This process is a modification of that 

 described by Wright {Brit. Med. Journ. , 

 p. 355, 1898), to which the reader is 

 referred for fuller details. 



It is advisable to use a dilution of 

 I in 20 if the macroscopic method is 

 used. 



I now use dead cultures almost ex- 

 clusively in routine work. They are 

 always ready, and they do not vary in 

 sensitiveness as living cultures do. The 

 method I now use is simplicity itself, 

 and is specially suited for general 

 practitioners, since it requires abso- 

 lutely no manipulative skill and gives absolutely accurate 

 results. 



The method is, briefly, as follows : I prepare a number of small 



Fig. 24. — Showing Method 

 OF FILLING Pipette. 



a Is the mark on the tube ; 

 b, the serum ; c, c, c, the 

 columns of emulsion, sepa- 

 rated by the air-bubbles, 

 d, d, d; c is the cotton- 

 wool plug. 



