276 FERMENTS AND ANTIFERMENTS 



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. 



Considerable experience is required in making these readings, and 

 the novice should practise well before conducting diagnostic tests. 



Individual readings by different persons may vary 0.02, and in 

 order to secure absolute certainty Abderhalden gives 0.04 as the limit 

 for error. 



A large margin for error will result if the primary reading is taken 

 when the tube is cold, as it is immediately after being filled. Only that 

 reading taken after the tube has been in the incubator for at least one or 

 two hours is to be taken as the guide for determining the amount of 

 digestion according to the degree of rotation. 



The greatest source of error lies in the observer himself. One must 

 be trained to make the readings in about thirty seconds; the eye soon 

 grows tired, and the readings are then unreliable. 



PRACTICAL VALUE OF ABDERHALDEN'S PREGNANCY TEST 

 1. It may be definitely stated that this test has failed to establish 

 itself as possessing value in the diagnosis of pregnancy. When per- 



