330 FREDERICK A. WOLF AND I. V. SHUNK 



upon it is ready for use. The danger of contamination from 

 this procedure, as judged by experience in making several thou- 

 sand tubes of media, is no greater than when the tubes are steri- 

 Mzed after the media has been placed in them, as is usually done. 

 In summary, this procedure removes the necessity of sterilization 

 after adjustment of reaction, eliminates the chances of change of 

 reaction or of other chemical changes which may be hastened by 

 a rise in temperature, and does not, within a wide range, destroy 

 the jellifying powers of the agar or gelatin. 



CONCLUSION 



Agar or gelatin media, if cooled before being made acid or 

 alkaline, will jelHfy at hmits far beyond pH concentrations 

 tolerated by microorganisms. They may be manipulated so as 

 to avoid contamination during adjustment of reaction and need 

 not be subsequently sterilized. 



REFERENCES 



Clark, W. M., and Lubs, H. A. 1917 The colorimetric determination of hydro- 

 gen ion concentration and its applications in bacteriology. Jour. 

 Bact., 2, 1-34, 109-136, 191-236, f. 1-8. 



Fellers, C. D. 1916 Some bacteriological studies on agar. Soil Sci., 2, 255- 

 290. 



Fellers, C. D. 1917 The analysis, purification, and some chemical properties 

 of agar-agar. Jour. Indus. Eng. Chem., 8, 1128-1132. 



Fred, E. B., and Davenport, Audrey 1918 Influence of reaction on nitrogen 

 assimilating bacteria. Jour. Agr. Res., 14, 317-336. 



Webb, R. W. 1919 Germination of the spores of certain fungi in relation to 

 hydrogen ion concentration. Ann. ]Mo. Bot. Garden, 6, 201-222. 



