THE PREPARATION OF CULTURE MEDIA 37 



adjustment of the apparatus the bent-down extremity 

 of the needle is made to dip into the colony, and on 

 raising it again, it emerges with some of the material 

 remaining attached, which can then be further inocu- 

 lated as desired. The instrument is obtainable from 

 'Calderoni & Co. of Deakgasse, Budapest, for 40s. 



Unna's instrument, which is of simpler and less costly 

 construction, consists of a short metallic tube into one 

 extremity of which a sewing needle can be axially fixed 

 by means of an arrangement similar to that used in 

 pencil-holders, whilst the other end of the tube can be 

 screwed on in place of the microscope lens. The lens 

 after being accurately centred on the colony in question 

 is exchanged for the instrument, and if the latter is 

 properly constructed the needle-point will now be verti- 

 cally over the colony ; on then screwing down the micro- 

 scope-tube the point of the needle will dip exactly into 

 the colony previously centred with the lens. This 

 'bacterial-harpoon,' as it is called, can be obtained from 

 Zeiss of Jena for 5s. 



Test-tube inoculations. A small quantity of the living 

 material to be inoculated is taken on the point of a sterile 

 platinum-needle, and the gelatine-tube into which it is 

 to be introduced is held in the left hand, mouth down- 

 wards. The cotton-wool stopper having been pre- 

 viously singed, is now removed, and is held also in the 

 left hand between the third and fourth fingers, care 

 being taken that the part of the stopper which goes 

 inside the tube does not come in contact with the hand 

 or any other object. The platinum-needle is then quickly 

 inserted or stuck into the gelatine and removed, the 

 cotton-wool stopper being then replaced. The tube 

 should be held mouth downwards during the whole 

 operation, so as to minimise the chance of contamina- 

 tion with aerial micro-organisms. 



