GENERAL BACTERIOLOGICAL DIAGNOSIS 115 



of another slide a film is made which is then dried and is ready 

 for staining. Films containing staphylococci are stained either 

 by Leishman's stain (q.v.) or with carbol-thionin blue. In the 

 former case no fixation is necessary, in the latter it is usual to 

 fix in saturated perchloride of mercury for 1| minutes, wash in 

 water and then stain. With tubercle films the following is the 

 procedure : the film is fixed for two minutes in perchloride of 

 mercury, washed thoroughly, stained with carbol-fuchsin as 

 usual, decolorised with 2'5 per cent sulphuric acid, cleared with 

 4 per cent acetic acid, counterstained with watery solution of 

 methylene-blue, and dried. 



In applying the technique two preparations are made, in both 

 of which the same emulsion and the same leucocytes are 

 employed, but in one of which the bacteria have been exposed 

 to the serum of the infected individual under observation, and 

 in the other to that of a normal person usually the observer 

 himself. Each of these is now examined microscopically with 

 a movable stage, the number of bacteria in the protoplasm of 

 at least 50 polymorphonucleated leucocytes is counted and an 

 average per leucocyte struck ; the proportion which this average 

 in the case of the abnormal serum bears to the average in the 

 preparation in which the healthy serum was used, constitutes the 

 opsonic index, that of the healthy serum being reckoned as 

 unity. The reliability of the method of course depends on the 

 phagocytic activity of the 50 cells counted representing the 

 phagocytic activity of all the cells in the preparation. 



GENERAL BACTEEIOLOGICAL 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 (1) of a micro- 

 scopic 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 (1) that 

 every precaution must be adopted to prevent the material from 



