594 S. H. AYERS, C. S. MUDGE AND PHILIP RUPP 



The results obtained by the addition of NaCl and HC1 to 

 the wash water are interesting. Various amounts of salt and 

 acid were used, their use having been suggested by Dr. Zoller 

 of these laboratories. The best results were obtained as follows : 

 20 grams of shred agar was added to 1000 cc. of distilled water 

 containing 10 grams of NaCl and 5 cc. of N/10 HC1. This 

 was allowed to stand for six hours at room temperature, then 

 the salt and acid solution was poured off and replaced by 1800 

 cc. of fresh distilled water. This was allowed to stand 18 hours, 

 which made the washing period twenty-four hours. The agar 

 was then poured on a cotton-flannel cloth in a funnel and washed 

 with 500 cc. of distilled water, then allowed to drain and as 

 much water pressed out by hand as possible. The agar was 

 finally air dried. 



The agar treated in this manner showed a lower calcium and 

 magnesium content than any of the others. Reference to the 

 table shows that it contained 0.39 per cent of CaO, and 0.08 per 

 cent MgO, while the protein content was reduced from about 

 2.2 per cent to 1.35 per cent. 



Media made with this agar did not, however, give quite such 

 satisfactory counts as that made with washed agar, but its use 

 has not been tried out very extensively. This method of wash- 

 ing, however, has possibilities of considerable value. The 

 principal point of interest at present in connection with the use 

 of NaCl and HC1 is the fact that they assist in the removal of 

 the calcium and magnesium salts. 



We were very much interested in the results obtained with 

 washed agar. It was valuable to us because it made possible 

 a milk-powder agar medium which would stand sterilization 

 without precipitation of the phosphates, but the fact that higher 

 bacterial counts were often obtained when it replaced ordinary 

 shred agar in the standard extract medium led us to wonder 

 just what might be the explanation. 



In connection with the milk-powder medium it had been 

 noticed that the presence of too much phosphate often lowered 

 the bacterial counts. Even the increase from 0.1 per cent to 

 0.2 per cent seemed to have a marked effect. Besides this, in 



