CHAPTER V. 



SEPARATION OF MICRO-ORGANISMS FROM THE 



TISSUES. 



66. In order to carry out pure cultivations, as described in the pre- 

 ceding chapters, it is essential to be able to separate the seed material 

 which it is desired to cultivate, and inoculate it in suitable media 

 uncontaminated by foreign elements. Some differences of method 

 must be noticed in this respect, according as the tissues supposed 

 to contain organisms are living or dead. 



i. — From Living Tissues. 



67. (a.) Blood. — In the case of the human subject this is usually 

 taken from the finger or from the ear. In either case the skin is first 

 cleansed with warm water and soap, then purified with a one per cent, 

 solution of perchloride of mercury, and lastly washed with absolute 

 alcohol. In the case of the finger, the venous return is hindered by 

 the application of an elastic band, and vascular engorgement of the 

 part ensues. The sterile surface is then pricked with a needle that 

 has previously lain for several minutes in absolute alcohol, and the 

 drop of blood which exudes is collected on the looped end of a sterile 

 platinum wire, and can be at once used for inoculation as already 

 described. In animals the same method may be employed, first 

 shaving the part to be put into requisition ; it is more usual, how- 

 ever, to kill the animal, and obtain blood before coagulation has set 

 in, as described in the next section. 



(/>.) Solid Tissues. — Here the best method is to make use ofDuch- 

 enne's needle, which has been previously thoroughly sterilised by super- 

 heating (see § 68, p. 118). The skin surface through which it is intro- 

 duced is sterilised beforehand, as already described {vide supra), and 

 the minute portion of tissue thus obtained is at once transferred to 

 the tip of a sterile platinum wire, inoculated into a suitable nutrient 

 medium, and, if need be, incubated. 



