134 GENERAL BACTERIOLOGICAL DIAGNOSIS 



capsule of the organ is cut through, with a sterile knife, the 

 incision being further deepened by tearing. In this way a 

 perfectly uncontaminated surface is obtained. Hints are often 

 obtained from the clinical history of the case as to what the 

 procedure ought to be in examination. Thus, as a matter of 

 practice, cultures of tubercle ani often of glanders bacilli can 

 be readily obtained only by inoculation experiments. 



Routine Procedure in Bacteriological Examination of 

 Material. — In the case of a discharge regarding which nothing 

 is known, the following procedure should be adopted : (1) 

 Several cover-glass preparations should be made. One ought 

 to be stained with saturated watery methylene-blue, one with 

 a stain containing a mordant such as Ziehl-Neelsen carbol- 

 fuchsin, one by Gram's method. (2) A series of agar smear 

 plates or successive strokes on agar tubes (p. 58) should be 

 made and incubated at 37° C. The clinical history, e.g., where 

 there is suspicion of pneumococcus or meningococcus infec- 

 tion, may suggest that special media should be employed. 

 In every case when an unknown disease is being investi- 

 gated, some of the material should be subjected to methods 

 suitable to the growth of anaerobic bacteria. If microscopic 

 investigation reveals the presence of bacteria, it is well to 

 keep the material till next day, when, if no growth has 

 appeared in the incubated agar, some other culture medium 

 {e.g., blood, serum or agar smeared with blood) may be em- 

 ployed. If growth has taken place, say in the agar plates, 

 one with about two hundred or fewer colonies should be made 

 the chief basis for research. In such a plate the first question 

 to be cleared up is : Do all the colonies present consist of the 

 same bacterium 1 The shape of the colony, its size, the appear- 

 ance of the margin, the graining of the substance, its colour, 

 etc., are all to be noted. One precaution is necessary, namely, 

 it must be noted whether the colony is on the surface of the 

 medium or in its substance, as colonies of the same bacterium 

 may exhibit differences according to their position. The 

 arrangement of the bacteria in a surface colony may be still 

 more minutely studied by means of impression preparations. 

 A cover-glass is carefully cleaned and sterilised by passing 

 quickly several times through a Bunsen flame. It is then placed 

 on the surface of the medium, and gently pressed down on the 

 colony. The edge is then raised by a sterile needle, it is seized 

 with forceps, dried high over the flame, and treated as an 

 ordinary cover-glass preparation. In this way very characteristic 

 appearances may sometimes be noted and preserved, as in the 



