I AND ii MILK AND POTATO TUBES 89 



clave at 120 C. for twenty minutes: a single sterilisation 

 suffices, but overheating must be carefully avoided. 



(4) Fill test-tubes in the usual manner, and sterilise them 

 in the autoclave. 



IX. POTATO TUBES. 



(1) Take sound large potatoes and scrub them thoroughly. 



(2) Cut off the ends, and with a cork-borer bore solid 

 cylinders out of the potatoes. 



(3) These cylinders should measure 3|- to 4 in. in length, 

 and just fit the lumen of the test-tubes. 



(4) By means of a diagonal cut divide them in two, 

 and wash them thoroughly in water, which may be slightly 

 alkaline. 



(5) Now take sterilised test-tubes, and at the bottom 

 of each place a little moistened cotton-wool. Into each 

 tube drop a piece of potato, with the broad end downwards, 

 and replace the cotton-wool plugs. 



(6) Sterilise in the autoclave for half an hour to one 

 hour at 120 C., covering the tubes up with stout tinfoil. 

 Avoid overheating, otherwise the potatoes will lose their 

 natural white colour and become sodden in appearance. 



X. MILK TUBES. 



(1) Neutralise " separated milk," if it be acid, and fill a 

 number of sterile test-tubes, in the ordinary manner, using 

 a separating funnel. 



(2) Sterilise on three successive days in the steamer. 



