158 TEXT-BOOK OF BACTERIOLOGY. 



should be removed and the skin should be freed from accidental im- 

 purities with a ^f, solution of corrosive sublimate. The instru- 

 ments must be reliably sterilized and should be cleaned again imme- 

 diately after being used. 



This is difficult only in the case of the syringes employed. Much 

 ingenuity has been expended in the attempt to devise an instru- 

 ment in which it shall be possible to sterilize the piston. Koch has 

 cut the Gordian knot by dispensing with the piston altogether. 

 His syringe is of glass and is, together with its needle, heated in the 

 hot-air oven each time before being used. The best way is to put 

 it into a wide test-tube. The pressure is exercised by a small India- 

 rubber ball, which we fix upon the syringe, and which, as it does 

 not come into direct contact with the inoculating fluid, requires no 

 sterilizing. 



Another instrument very suitable for our purposes is that 

 recently invented by Stroschein. Two short tubes, resembling test- 

 tubes, are placed one within the other in such a manner that the 

 inner one, which is somewhat shorter and narrower, is held in con- 

 nection with the outer one by a stiff, broad India-rubber ring. The 

 inside tube has at one end a continuation upon which the needle 

 fits, and at the other end a small aperture connecting it with the 

 space between the inner and outer tube. If, with a twisting motion, 

 the two tubes are drawn asunder as far as the India-rubber ring 

 win allow, a partial vacuum is produced, and if during this time 

 the needle be dipped into the injecting fluid, the latter will be sucked 

 up into the inner tube. A pressure with the thumb now causes one 

 tube to ride over the other. This little apparatus is easily con- 

 structed, cheap, easily sterilized, and very convenient, especially 

 as it can be worked with one hand only. 



