104 AIDS TO BACTERIOLOGY 



properties by degrees, and should never be used if it is 

 older than three months. 



Antityphoid vaccine does not protect against the para- 

 typhoids (q.v.). Inoculation has proved to be quite a 

 harmless procedure, the great majority of men inoculated 

 experiencing nothing more than ' inoculation fever.' 

 Very occasionally it starts pyogenic organisms, already 

 lurking in the body, into activity. 



Bacteriological Diagnosis Blood Culture. Two to five 

 c.c. of blood are withdrawn from a superficial vein with 

 a sterile syringe, and small flasks of broth (25 to 50 c.c.) 

 are inseminated, each with 1 to 2 c.c. of the blood, and 

 incubated. This method serves to differentiate cases of 

 paratyphoid from true typhoid by the differences in the 

 bacilli isolated. It is useful for diagnosis during the first 

 week. 



Widal's Reaction (see p. 19). The lobe of an ear is 

 Washed with ether or some other suitable liquid. With 

 a straight, spear-pointed surgical needle a prick is made 

 into the lobe and the blood collected in a capillary tube, 

 preferably sterile. An ordinary vaccine tube does very 

 well. The blood should form a continuous column in 

 the tube. The ends of the tube should be cautiously 

 sealed in the flame, dry end first, care being taken that 

 the blood is so far away from the ends as not to become 

 heated. It is better if the tube can be centrifuged, so 

 as to obtain a clear serum; if this cannot be done, it 

 will be found that after a few hours, on breaking off the 

 ends of the tube, a string of clot and some serum can be 

 blown out on to a glass slide, and the serum with some 

 corpuscles collected in another capillary tube, or in the 

 diluting pipette to be described immediately. If the 

 tube has been centrifuged, it is broken off at the junction 

 of serum and corpuscles, and the clear serum blown out. 



A haemocytometer pipette may be used for diluting, or 

 a pipette may be made by drawing out a piece of glass 

 tubing in the blowpipe flame. A little of the serum is 

 drawn up into it, a mark made on the glass at the upper 

 limit of the serum, and the serum blown out into a watch 

 glass. Then any desired number of similar volumes of 

 diluting fluid (O7 per cent, salt solution) are added to the 

 serum, and the whole mixed. 



Alternatively, Delepine's method may be adopted: 



