The Isoelectric Point of the Dick Toxin.

In the course of experiments having for their purpose purification of Dick toxin it became desirable to ascertain the electrical charge carried by the toxic material. This point seemed worthy of investigation not only because of our own immediate needs for such information, but also because the electrical charge borne by a toxin is an important factor in filtration, adsorption, flocculation, etc.

The method described by Krueger, Ritter and Smith, 1 based upon electrophoresis of the test substance into agar and subsequent resuspension in some appropriate menstruum, was employed. Toxin∗ of high titre was adjusted to the required pH value with N/10 NaOH or HCl, placed in the two cells of the apparatus and exposed to a current of 70-85 v. and 5-12 milliamps. for 20 hours. At the end of this time the agar cylinders from anode and cathode were removed and triturated with 10 cc. normal saline solution for 1 hour. The extracts so obtained were then made up in 1/100 dilutions with normal saline and injected in quantities of 0.1 cc. into the skin of individuals known to be Dick positive. Each test patient also received a control injection, i. e., 0.1 cc. of a 1:10,000 dilution of toxin previously adjusted to the pH at which the test was run, maintained at this C_H+ for the same length of time as the toxin in the apparatus and neutralized before injection. This injection served to detect inactivation of the toxin by acid or alkali and also furnished us with a criterion by which to read the other skin reactions. We found it necessary to employ in the cataphoresis cells a gel containing not more than 0.4% purified agar. Percentages higher than this did not permit the toxin to migrate.