Abstract
In order to estimate the specific protein content of an unknown solution, 2 methods of precipitin titration are in use. Successive dilutions of the unknown may be mixed with a constant amount of specific antiserum, and the maximum dilution giving a demonstrable precipitin reaction may be determined. This dilution is compared with the maximum dilution of a known or standard protein solution giving the same end-reaction. For example, if the unknown gives an end-reaction in the dilution 1:1000, while the corresponding reading with the standard solution is 1:10,000, the conclusion is drawn that the unknown contains 10% of the specific protein of the standard, interfering factors, of course, being experimentally ruled out.
The method favored by many botanists and zoologists, however, is to estimate the amount of precipitate in some arbitrary dilution, preferably by means of a hematocrite, 1 the assumption being that equal precipitates indicate equal amounts of specific protein.
Applying these methods to a study of the parenteral history of alien proteins we have obtained contradictory and paradoxical results, the details of which have not yet been published. 2 As an illustration, the following data are cited.
If 2 cc. horse serum per kilo of body weight are injected intravenously into a normal dog, and if blood samples are withdrawn from this dog: (i) immediately before the injection, (ii) 15 minutes after the injection, and (iii) at the end of about 14 days, parallel titrations of the sera of the resulting blood samples by means of an ice-chest ripened (14 to 30 days) specific rabbit precipitin give the readings recorded in Fig. 1.
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