114 MICROSCOPIC METHODS. 



alternative method is as follows : The surface is sterilised by 

 soaking it well with I to 1000 corrosive sublimate for half an 

 hour. It is then dried, and the 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 and often of 

 glanders bacilli can be easily obtained only by inoculation experi- 

 ments. Typhoid bacilli need hardly be looked for in the faeces 

 after the first ten days of the disease, and so on. 



Routine Procedure in Bacteriological Examination of Material. 

 In the case of a discharge regarding which nothing is known 

 the following procedure should be adopted: (i) Several cover- 

 glass preparations should be made. One ought to be stained 

 with saturated watery methylene-blue, one with a stain contain- 

 ing a mordant such as Ziehl-Neelsen carbol-fuchsin, one by 

 Gram's method. (2) (a) Gelatin plates should be made and kept 

 at room temperature, (b) a series of agar plates or successive 

 strokes on agar tubes (p. 57) should be made and incubated at 

 37 C. Method (b) of course gives results more quickly. If 

 microscopic investigation reveals the presence of bacteria, it is 

 well to keep the material in a cool place 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 

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

 with about 200 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 ? 

 The shape of the colony, its size, the appearance of the margin, 

 the graining of the substance, its colour, etc., are all to be noted. 

 One precaution is necessary, viz., 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 



