HILL, H. W. The Mathematics of the Bacterial Count. _Public Health Reports and Papers_, 33, 1907, 110. Bibliography 213: ITANO, A. The Relation of Hydrogen Ion Concentration of Media to the Proteolytic Activity of Bacillus Subtilis. _Bulletin 167_, 1916, Mass. Agric. Ex. Station. Bibliography 214: KENDALL, A. I. and WALKER, A. W. The Isolation of Bacillus Dysenteriae from Stools. _Jour. Med. Research_, 23, 1910, 481. Bibliography 215: KINYOUN, J. J. and DEITER, L. V. On the Preparation of Endo’s Medium. _Amer. Jour. Public Health_, n. s. 2, 1912, 979. Bibliography 216: LEVINE, M. On the Significance of the Voges-Proskauer Reaction. _Jour. of Bacteriology_, 1, 1916, 153. Bibliography 217: LUBS, H. A. and CLARK, W. M. On Some New Indicators for the Colorimetric Determination of Hydrogen-ion Concentration. _Jour. Wash. Acad. of Sciences_, 5, 1915, 609. Bibliography 218: MCCLENDON, J. F. New Hydrogen Electrodes and Rapid Methods of Determining Hydrogen Ion Concentrations. _Amer. Jour. of Physiology_, 38, 1915, 180. Bibliography 219: MCCLENDON, J. F. A Direct Reading Potentiometer for Measuring Hydrogen Ion Concentrations. _Amer. Jour. of Physiology_, 38, 1915, 186. Bibliography 220: MCCRADY, M. H. The Numerical Interpretation of Fermentation-tube Results. _Jour. Inf. Diseases_, 17, 1915, 183. Bibliography 221: NOYES, H. A. Agar Agar for Bacteriological Use. _Science_, n. s. 44, 1916, 797. Bibliography 222: ROGERS, L. A., CLARK, W. M. and DAVIS, B. J. The Colon Group of Bacteria. _Jour. of Inf. Diseases_, 14, 1914, 411. Bibliography 223: ROGERS, L. A., CLARK, W. M. and EVANS, A. C. The Characteristics of Bacteria of the Colon Type Found in Bovine Feces. _Jour. of Inf. Diseases_, 15, 1914, 99. Bibliography 224: ROGERS, L. A., CLARK, W. M. and EVANS, A. C. The Characteristics of Bacteria of the Colon Type Occurring on Grains. _Jour. of Inf. Diseases_, 17, 1915, 137. Bibliography 225: SMITH, H. M. The Seaweed Industries of Japan. _Bulletin of the Bureau of Fisheries_, 24, 1904, 135. Bibliography 226: SÖRENSEN, S. P. L. Enzymstudien. _Biochem. Ztschr._, 21, 1909, 131 and 201. Bibliography 227: WHIPPLE, G. C. On the Necessity of Cultivating Water Bacteria in an Atmosphere Saturated with Moisture. _Tech. Quart._, 12, 1899, 276. Bibliography 228: WHITTAKER, H. A. The Source, Manufacture and Composition of Commercial Agar-agar. _Jour. Amer. Pub. Health Assoc._, n. s. 1, 1911, 632. Bibliography 229: CLARK, W. M. and LUBS, H. A. The colorimetric determination of the hydrogen-ion concentration of bacteriological culture media. _Jour. Wash. Acad. Sciences_, 6, 1916, 483. Bibliography 230: CLARK, W. M. and LUBS, H. A. The colorimetric determination of hydrogen-ion concentration and its application in bacteriology. _Jour. of Bact._, 2, 1919, 1 and 109. Bibliography 231: