60 



A MANUAL OF BACTEEIOLOGY 



a half and steam for one hour on two successive days. 



The milk is usually tinged with litmus before tubing, 



forming litmus milk. 



Potatoes. Choose sound potatoes, and scrub them well 



with water to remove dirt. Cut off the ends, and with a 

 C^*. cork-borer, slightly smaller than the test- 

 tubes which are used, bore through the 

 potato so that a cylindrical piece is re- 

 moved. Push this out of the borer, and 

 divide it into two portions by a very 

 oblique transverse cut, so that two wedge- 

 shaped pieces are obtained, and in this 

 manner prepare as many pieces as there are 

 tubes to be filled. Place them in a basin 

 under the tap, and allow the water to flow 

 over them for about two hours. This pre- 

 vents the darkening of the potato in the 

 subsequent steaming, as does also the use 

 of a silver borer. The test-tubes for the 

 potato- wedges are prepared as follows : 

 After plugging and sterilising in the ordi- 

 nary way /introduce' a small pledget of steri- 

 lised wool into each, push to the bottom, 

 and moisten with a little sterilised distilled 



^^ water. Drop the potato-wedges into the 

 FIG. 9. Roux's . , i T .,. , , 



tube for potato. tubes > P lu g> and sterilise by steaming for 

 three-quarters of an hour on two succes- 

 sive days (Fig. 8, B). The object of the moist wool 

 is to prevent drying, and for the same purpose Roux's 

 tubes (Fig. 9) may be used, the lower bulb being filled with 

 water. 



Blood-serum. Clean some glass jars of about 1 to 

 3 litres capacity, plug with wool, and sterilise in the 

 steamer for an hour on three successive days. Bleed 

 a horse, with aseptic precautions, and catch the blood 



