TECHNICAL APPENDIX. 183 



bouillon agar generally contains traces of grape 

 sugar, we have for some time made a milk-sugar 

 agar which is free from grape sugar, according to the 

 plan described under A. 



11. Glycerin agar. To the nutrient agar is added 

 five per cent glycerin, the mixture poured into test 

 tubes and sterilized. 



12. Sugar-chalk agar. Mix melted sugar agar 

 with finely powdered, dry, sterilized carbonate of 

 lime until the mixture becomes cloudy and opaque, 

 inoculate the bacteria into it, and pour out in plates. 



13. Potatoes. After careful washing the potatoes 

 are peeled, cut into discs 1 cm. thick, and sterilized 

 several times in high Petri's dishes. We may also 

 perforate the peeled potato with a large cork borer 

 and divide che cylinder by an oblique cut into two 

 wedges. The pieces are then placed in a test tube 

 at the bottom of which is a little dry cotton (to ab- 

 sorb the water cf condensation) and sterilized several 

 times in the steam chamber. 



14. Blood serum. The blood, taken from the 

 slaughtered animal under proper precautions, is al- 

 lowed to stand for twenty -four hours in well cleaned 

 glass cylinders in the refrigerator; on the following 

 day the serum is removed by means of large sterile 

 pipettes. It is placed in bottles, one per cent chloro- 

 form is added, and is then allowed to stand for a few 

 weeks, being shaken occasionally. For use, we place 

 the serum, which has been poured into tubes, in the 

 incubating chamber for a few days in order that the 

 chloroform may escape completely. It is employed 

 either in the fluid state or after it has been made rigid 

 at a temperature of 65. 



