USE OF WASHED AGAR IN CULTURE MEDIA 593 



salts, and acidity. As the results show, the moisture content 

 of this agar was variable, but the content of calcium was no 

 lower than that of shred agar, although the magnesium had 

 been slightly reduced. The protein content, however, was about 

 50 per cent of that of shred agar. 



The analysis of washed agar showed a decided decrease in the 

 percentage of calcium and magnesium, and experiments were 

 made to determine the time required to wash the agar, starting 

 with 30 grams to 2000 cc. of water. Agar "A" was held twenty- 

 four hours. Agar "B" was held forty-eight hours, but after the 

 first twenty-four hours the 2 liters of water were replaced with 

 fresh water. Agar "C" was held seventy-two hours, the water 

 being removed and replaced with fresh distilled water at the 

 end of each twenty-four hours. The agar was air dried by spread- 

 ing it on filter papers after washing. 



It will be seen from the table that the moisture content of 

 the three lots of agar was very similar to that of shred agar. 

 The most interesting effect of washing was the reduction of the 

 calcium and magnesium salts. The forty-eight-hour period of 

 washing, which is the one we have used most extensively, reduced 

 the CaO from about 1.1 per cent to 0.7 per cent, and the MgO 

 from about 0.78 per cent to 0.39 per cent. The calcium and 

 magnesium content was reduced sufficiently by this treatment 

 to give satisfactory results in the milk-powder agar medium; 

 that is, enough was removed so that the phosphates did not 

 precipitate upon sterilization. Agar washed twenty-four hours 

 in the proportion of 30 grams to 2000 cc. of water was not 

 entirely satisfactory and, as the results show, there was but 

 little further reduction in the calcium and magnesium by washing 

 for seventy-two hours. 



It was found that by increasing the amount of distilled water, 

 good results could be obtained in twenty-four hours. When 

 30 grams of shred agar was held in 5000 cc. of distilled water 

 for twenty-four hours the calcium and magnesium content was 

 found to be 0.61 per cent and 0.43 per cent respectively, when 

 calculated on a moisture-free basis. 



