98 THE AMERICAN NATURALIST. [Vor. XXXIV. 
water and dividing the combined weight (2.111+) by the com- 
bined volume (2), which gives 1.056 —. For the third place in 
the table I added to 1 cc. of the original mixture 2 cc. of. pure 
water, 3.111 + divided by 3 giving 1.037, and so on. 
TABLE I. — SPECIFIC GRAVITY OF SUCCESSIVE DILUTIONS OF GUM- 
ARABIC SOLUTION. 
Starting with 1 cc. of the stock solution and adding water 1 cc. at a time, 
I gram gum arabic being reckoned as the equivalent of 0.7 cc. volume. 
Vol. 
added s: 1 3 3 4 5 G 7 a 9 
Sp. gr. 1.1114/1.056—-|1.037 |1.028 |1.022 |r.o185| 1.016 |1.014 |r.OI2 |I.OII 
Vol. 
added IO II I2 I3 I4 15 16 IT 18 19 
Sp. gr. |r.o10 |1.009 |1.0085| 1.008 |1.0074|1.007 | 1.0065|1.006 | 1.0058} 1.0055 
Vol. 
added 20 2I 22 23 24 25 26 27 28 29 
Sp. gr. |1.0053 |1.005 |1.0048 | 1.0046 | 1.0044 | 1.0042 | 1.0041 | 1.004 | 1.0038 | 1.0037 
Vol. 
added 30 31 32 33 34 35 36 37 38 39 
Sp. gr. |1.0036 |1.0034 | 1.0033 | 1.0032 |1.0031|1.003 |1.003 |1.003 |1.0029| 1.0028 
TABLE II. — MODIFICATION FOR USE WITH MINUTE ANIMALS. 
By starting with } cc. of the stock solution and adding -4 cc. of water at a time, 
there is a smaller interval between two steps than is possible by the method 
of Table I. 
Vol. | 
died o -33 .67 I 1.33 | 1.67 2 2.33 | 2.67 3 
Sp. gr. |.111. | 1.083 (1.0667 1.056 |1.047 |t.o41 | 1.037 |1.033 |1.030 | 1.028 
Vol. 
addea | 3°33 | 367| 4 | 433 | 4.67| 5 | 533 | 567 | 6 | 6.33 
Sp. gr. |1.025 | 1.024 | 1.022 | 1.021-|1.019+/1.018+] 1.017 | 1.0165 | 1.016-| 1.015 
Vol. 
added | 997 | 7 | 7-33 
Sp. gr. |1.0145 | 1.014 | 1.013 
