GENERAL BACTERIOLOGICAL DIAGNOSIS. 121 



is sucked up after it to separate it from the bacterial emulsion, which is 

 then drawn up in the same quantity ; the diluted serum will then occupy 

 the position kl. The fluids are then drawn several times up into the 

 bulb and returned to the capillary tube so as to mix, and finally blown 

 carefully down close to the lower end, which is then sealed off. The 

 sediment collects at the lower extremity. 



GENERAL BACTERIOLOGICAL DIAGNOSIS. 



Under this heading we have to consider the general 

 routine which is to be observed by the bacteriologist when 

 any material is submitted to him for examination. The 

 object of such examination may be to determine whether 

 any organisms are present, and if so, what organisms ; or the 

 bacteriologist may simply be asked whether a particular 

 organism is or is not present. In any case his inquiry 

 must consist (i) of a microscopic examination of the 

 material submitted ; (2) of an attempt to isolate the 

 organisms present ; and (3) of the identification of the 

 organisms isolated. We must, however, before considering 

 these points look at a matter often neglected by those who 

 seek a bacteriological opinion, viz. : the proper methods of 

 obtaining and transferring to the bacteriologist the material 

 which he is to be asked to examine. The general principles 

 here are (i) that every precaution must be adopted to 

 prevent the material from being contaminated with ex- 

 traneous organisms; (2) that nothing be done which may 

 kill any organisms which may be proper to the inquiry ; 

 and (3) that the bacteriologist obtain the material as soon 

 as possible after it has been removed from its natural 

 surroundings. 



The sources of materials to be examined, even in 

 pathological bacteriology alone, are of course so varied that 

 we can but mention a few examples. It is, for instance, 

 often necessary to examine the contents of an abscess. 

 Here the skin must be carefully purified by the usual 

 surgical methods ; the knife used for the incision is prefer- 

 ably to be sterilised by boiling, the first part of the pus 

 which escapes allowed to flow away (as it might be spoiled 



