170 EXPERIMENTAL INOCULATIONS 



(b) Cultures on solid media. A small incision may be made in the skin 

 and then a wire, charged with the micro-organisms by scraping the surface 

 of the medium, rubbed into the tissues. But it is more usual to make an 

 emulsion by rubbing up some of the material in sterile water or broth and 

 then to inoculate the emulsion with a syringe. 



Scrape the surface of the medium with a stout platinum wire and transfer 

 the growth to a sterile watch-glass containing a little sterile water and stir 

 it about until an homogeneous emulsion is obtained. If the culture be difficult 

 to break up as, for example, a growth of the tubercle bacillus and does not 

 mix with water, it should be ground up as described below (d). 



(c) Pus. As a rule, pus is too thick to be inoculated undiluted. Transfer 

 a few drops of the pus with a pipette to a sterile watch-glass, add a little 

 sterile normal saline solution (O8 per cent, aqueous solution of sodium chloride) 

 or broth and mix them thoroughly with the end of the pipette. 



(d) Fragments of organs. For the method of collecting fragments of 

 internal organs, portions of the central nervous system, etc., see Chap. XI. 



Transfer the material to a sterile watch-glass and break it up with a sterile 

 glass rod. When the tissue is reduced to a fine paste add a little sterile normal 

 saline solution drop by drop from a pipette, and mix until a quite homo- 

 geneous suspension is obtained. 



It is often necessary to filter the suspension through a small piece of pre- 

 viously sterilized fine muslin to get rid of little lumps. This precaution is 

 very necessary when the emulsion has to be inoculated intra-venously, in 

 order to avoid the formation of an embolus. 



When a very tough material has to be dealt with such as tuberculous or 

 leprous nodules, it should be cut up into quite small fragments with sterile 

 scissors, ground up in a sterile mortar with some fine sterile sand x (p. 155) 

 and a fluid emulsion made by adding sterile normal saline solution drop by 

 drop : the emulsion is then filtered through fine, sterile muslin before being 

 inoculated. 



When a larger quantity of material has to be emulsified, BorrePs broyeur 

 will be found useful. With this machine fine powders or emulsions can be 

 obtained without contaminating the material and without exposing the 

 operator to the inhalation of dust containing pathogenic organisms. 



3. Technique of inoculation. 



General rules. Before inoculating an animal shave the hair and cleanse 

 the skin of the part. 



The hair may be cut very short with a pair of curved scissors but it is better to 

 shave the skin. For delicate inoculations it is preferable to epilate the hairs with 

 one of the following solutions : 



1. Recently slaked lime, - 2 parts. 

 Water, - 3 



Pass a stream of hydrogen sulphide through the emulsion, shaking it frequently, 

 until it is saturated. Apply the paste to the part to be epilated and after a few 

 minutes wash it off with water and a nail brush. 



2. Sodium sulphide, - 3 parts. 

 Powdered quicklime, - 10 ,, 

 Starch, - 10 



Mix into a powder. When required for use, add sufficient water to a little of the 

 powder to form a soft paste and apply it to the skin. After 3 or 4 minutes' applica- 

 tion the hair is removed. 



I 1 Sand was used as a triturating agent by Cobbett in his earlier experiments on tuber- 

 culosis but was almost immediately given up. A little patience is all that is required to 

 grind up even a tough tuberculous lesion.] 



