262 FERMENTS AND ANTIFERMENTS 



evaporation of the solution under diminished pressure and at 40 C. A special drop 

 funnel delivers the peptone solution drop by drop and thus prevents foaming. 



The yellowish, syrupy residue that remains is covered with 100 volumes of 

 methyl alcohol and boiled. The boiling hot solution is then filtered through five 

 thicknesses of filter-paper into five volumes of cold ethyl alcohol, which is kept in 

 ice water. Precipitation may be accomplished by the addition of ether. Just as 

 soon as the precipitate has formed it is filtered out, preferably through a porcelain 

 filter. The filter is then placed in a vacuum desiccator, and after one or two days 

 the peptone is dry and easily removed and weighed. 



A 10 per cent, solution in 0.9 per cent, salt solution is prepared, and the rotation 

 determined. If the rotation is more than 1, the solution is diluted until the rota- 

 tion is 0.75. 



Testing the Peptone. One cubic centimeter of fresh, clear, hemo- 

 globin- and corpuscle-free serum from a man and an equal amount of a 

 5 to 10 per cent, solution of the peptone are placed in a sterile polaris- 

 cope tube, warmed to 37 C., and the rotation read. If marked changes 

 occur, the peptone is not free from sulphuric acid or barium hydroxid. 

 With the serum of pregnancy, readings should be taken each hour for 

 six hours, and then at intervals of from thirty-six to forty-eight hours. 

 It is well to test a number of pregnancy serums until a normal curve 

 can be charted. 



Peptones of other tissues and bacteria may also be prepared. 



The Polariscope. A perfect and delicate instrument is necessary, 

 that of Schmidt and Hansch, Berlin, being recommended by Abder- 

 halden. The instrument must be delicate enough to record differences 

 in rotation of 0.01, and be furnished with an electric incubator attach- 

 ment for keeping the tube at a constant temperature of 37 C. The 

 tubes may, however, be kept in a bacteriological incubator, removed, 

 quickly read, and then returned. 



The Test. One cubic centimeter of fresh and absolutely hemoglo- 

 bin- and corpuscle-free serum is placed in the polarization tube with 

 1 c.c. of a 10 per cent, solution of standardized placental peptone; suf- 

 ficient sterile saline solution is added to fill the tube. The tube is then 

 placed in an incubator at 37 C. for an hour, and a reading made. An- 

 other reading is taken an hour later, and the two readings should not 

 show more than a minute difference in rotation. Another reading is 

 made at the end of six hours, and others at intervals during the next 

 thirty-six or forty-eight hours. 



Reading the Reaction. In serums of pregnancy cleavage is usually 

 apparent at the end of six hours, and rotation may amount to 0.05 to 

 0.2 in thirty-six hours. With non-pregnant serums the rotation is 

 seldom more than 0.03. 



