APPENDIX 275 



in the autoclave for 15 minutes improves the rejuvenating 

 properties of the medium. They should be added to the 

 tubes after sterilization. 



Bacterial growth being very rapid in this medium, pre- 

 liminary rejuvenation at 37 C. should be concluded between 

 6 and 12 hours. 



HESSE AGAR 



Agar (absolutely dry) 4.5 gm. 



Peptone, Witte 10 gm. 



Liebig's Extract of Beef 5 gm. 



Salt 8.5 gm. 



Distilled Water 1000 c.c. 



Dissolve 4.5 gm. of dry agar in 500 c.c. distilled water 

 by heating over a free flame, making up loss in weight by 

 evaporation. Into another vessel 500 c.c. of distilled water 

 is poured and to this is added 10 gm. of peptone, 5 gm. of 

 Liebig's Beef Extract, and 8.5 gm. of salt. This is heated 

 until all is dissolved and the loss in weight by evaporation 

 is made up by adding distilled water. 



Add the two solutions together; boil 30 minutes; make 

 up loss in weight with distilled water, filter through absorb- 

 ent cotton held in the funnel by cotton flannel, passing 

 the filtrate through several times until perfectly clear. 

 Test the reaction; adjust, if necessary, to +1.0 per cent 

 normal acid, and tube, using 10 c.c. of medium in each 

 tube. Sterilize for 15 minutes at 120 C. (15 pounds 

 pressure) in an autoclave. Cool with running water and 

 store in an ice-chest the air of which is saturated with 

 moisture. 



CONRADI-DRIGALSKI MEDIUM 



These authors have modified lactose litmus agar by 

 adding to it nutrose and crystal violet and by using 3 per 

 cent of agar instead of i per cent. The crystal violet 

 strongly inhibits the growth of many other bacteria, especially 

 cocci, which would also color the medium red; the 3 per 



