78 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



mix it with the two units in the second watch-glass, and again 

 take one unit from the first mixture and mix it with the four 

 units in the fourth watch-glass. This will give you three mixtures 

 of I in lOj I in 30, and i in 50 respectively. 



Suck up part or the whole of the i in 10 dilution into the 

 pipette marked i, then suck up a little air and seal the tip of the 

 pipette in the flame. When it is cool it is advisable to stand it in 

 a test-tube of i in 20 carbolic for safety. 



Take up the i in 30 in the pipette marked 2, draw the column 

 of fluid from the tip, as before, and seal the end. 



Take up the i in 50 in the pipette marked 3 and seal. 



Lastly, suck up a column of the typhoid emulsion unmixed 

 with serum into the fourth pipette, and seal it. This is to act 

 as a control, to make sure that the emulsion does not clump and 

 settle spontaneously. This false clumping is, in the conditions 

 of the test as here described, much less common than when the 

 microscopic method is used. 



The tubes must now be incubated at the body temperature. 

 The simplest plan is to heat a large test-tube of water (or prefer- 

 ably of carbolic lotion) to the required point, insert the pipettes, 

 and place it in the incubator. If this is not at hand, the test-tube 

 may be prepared as before, and occasionally warmed over the 

 flame as it cools. The reaction is often complete in ten minutes, 

 usually in half an hour, and never need be watched for more than 

 one hour, provided it is incubated as described. The reaction can 

 be carried out at the room temperature, but is much slower and 

 not so satisfactory. 



Examine the tubes from time to time. In a negative reaction 

 the bacilli will very gradually settle to the bottom of the column 

 in all the pipettes, including the control, and after twelve to 

 twenty-four hours or more form a compact white mass. In a 

 positive reaction the appearances are very different. They are 

 first seen in the stronger dilution, then the weaker ones in order. 

 The fluid in the pipette showing them first becomes slightly 

 granular : this is best seen by looking at it by transmitted light, 

 holding the tube in front of a dark object over which the light 

 passes. After a time the granularity becomes easily visible, and 

 the bacilli have collected into flocculi most obvious to the naked 

 eye. These then settle to the bottom, forming a loose white or 

 greyish mass, which appears much more voluminous than the 

 compact mass formed by the settling of undamped bacilli. If a 



