APPENDIX 163 



It is essential that the solidification takes place below 100 C. 

 If steam is generated in large amount with air exclusion so that 

 the medium is heated to 100 C. (or only just below) before com- 

 plete solidification takes place, bubbles and cavities in the serum 

 will be formed and the medium spoilt. 



Luffler's Blood serum. This consists of three parts of blood 

 serum mixed with one part of I per cent, glucose broth. Other- 

 wise it is prepared as above. It is preferred by the writer to 

 ordinary serum for most purposes. 



Egg medium (for B. tuberculosis). Fresh eggs are washed 

 and then partially sterilized by dipping them, held in forceps, in 

 boiling water for about half a minute. They are opened with 

 aseptic precautions, and the contents poured into a sterile flask, 

 to which normal saline is added in the proportion of one part 

 to two parts of egg. The eggs and saline solution are then 

 thoroughly mixed in the flask, which should be of large size. 

 The medium is strained through muslin to remove air-bubbles, 

 and poured as quietly as possible into a flask with a side tube 

 near the bottom. The medium is added from this flask to 

 sterile test-tubes, when the latter are in a nearly horizontal 

 position, sufficient being added to make a good slope. Care 

 must be taken to avoid soiling the other parts of the test-tube. 

 The tubed medium is inspissated at So C. on two successive 

 days. 



Sugar media for fermentation testing. The power of bacteria 

 to ferment sugars, alcohols, etc. is best tested in double tubes 

 (Durham's tubes). The media in these tubes, after three days' 

 sterilization, should completely fill the inner tube. The stock 

 medium to which the different sugars are added is either ordinary 

 nutrient broth without the sodium chloride or without, in addition, 

 the Lemco (i.e. simply peptone water). The solution should be 

 faintly alkaline to litmus. 



This medium is made and sterilized in bulk and to appro- 

 priate quantities in a flask, are added, as required, the particular 

 sugar or alcohol, in amount to make 0*5 per cent in the finished 

 medium, and sufficient pure litmus solution to give a blue tint. 



II 2 



