156 BIOLOGY AND TECHNIQUE 



potatoes and soak them in tap water for from 12 to 24 hours, using about 

 500 grams to a liter of water. This mixture can be filtered, or, better, 

 heated before filtration. It may be used as an ingredient with or without 

 glycerin in ordinary broth or agar, or can be used with pepton and salt 

 added, as an independent culture medium. 



Glycerin Potato. In preparing glycerin potato the potato wedges are 

 treated as above, and are then soaked in a ten to twenty-five per cent aqueous 

 glycerin solution for one to three hours. A small quantity of a ten per 

 cent glycerin solution should be left in the tubes. In sterilizing these tubes, 

 thirty minutes a day in the Arnold after the sterilizer is hot, will sterilize 

 without altering the glycerin. 



Milk Media. Fresh milk is procured and is heated in a flask for fifteen 

 minutes in an Arnold sterilizer. It is then set away in the ice chest for 

 about twelve hours in order to allow the cream to rise. Milk and cream 

 are then separated by siphoning the milk into another flask. It is rarely 

 necessary to adjust the reaction of milk prepared in this way, since, if acid 

 at all, it is usually but slightly so. If, however, it should prove more than 

 1.5 per cent acid, it should be discarded or neutralized with sodium hydrate. 

 The milk may then be tubed either with or without the addition of an 

 indicator. Litmus gives the most satisfactory results in milk, but at the 

 present time is difficult to obtain. The Andrade indicator can be used also, 

 but usually discolors the milk somewhat. However, if fractional sterilization 

 is carefully carried out, the milk becomes yellowish, but acid production 

 shows up clearly by a distinct reddening of the medium. If the milk is 

 to be used for the differentiation of the anaerobic bacilli isolated from war 

 wounds, it is best not to add any indicator, since the type of coagulum 

 formed is a differential characteristic, and coagulation does not take place 

 readily when Andrade is present. 



SODIUM OLEATE AGAR (For Influenza Bacilli). Avery 19 has found that 

 sodium oleate will enhance the development of influenza bacilli, and at the 

 same time will inhibit many of the Gram-positive organisms commonly found 

 in sputum. 



A neutral solution of Kahlbaum's sodium oleate in water is prepared and 

 sterilized in the autoclave. Human or rabbit blood is defibrinated, centri- 

 fuged, the serum removed, and the volume made up to the original with 

 broth. 1 c.c. of the red blood cell suspension and 5 c.c. of the 2 per cent 

 sodium oleate solution are added to 94 c.c. of agar at 80 to 90 C. The 

 agar is preferably a 2 per cent hormone agar with a reatcion of P rt 7.4. 



Serum Media. Loeffler's Medium. Beef blood is collected at the 

 slaughter house in high cylindrical jars holding two quarts or more. It is 

 desirable that attempts should be made to avoid contamination as much as 



19 J. A. M. A. 1918, vol. 71, 2050. 



