126 PRECIPITINS 



only hare's serum and not rabbit's, for the reason that "Isoprecipitins," i.e., precipitins 

 against the same kind of animal, are, as a general rule, not developed. Similarly the 

 differentiation between human and ape's serum can be accomplished by the immuniza- 

 tion of apes with human serum. 



Attempts have also been made by means of the precipitation reaction 

 to determine the origin of albumin in urine, and the foreign proteids 

 circulating in the blood of artificially fed infants. 



The technique remains the same, independent of the purpose it is 

 employed for. It consists in the mixing of the clear precipitating serum 

 and the clear proteid, or albumin precipitinogen. 



Strongly precipitating antisera against proteid solutions are 

 Production prepared by methods analogous to those employed for the 

 of Proteid production of antibacterial sera. The use of rabbits is 

 Precipitating generally advised. The sera or proteid solutions should be 

 Antisera. s t e rile. Filtration through small porcelain niters may be 

 necessary. The injections may be made subcutaneously, 

 intraperitoneally, or intravenously. The subcutaneous route has no 

 advantage unless the substances to be used are contaminated; but then, 

 larger quantities are necessary. The intravenous path is the one of 

 choice. A single injection of a large dose (15 to 20 c.cm.), or three injec- 

 tions of moderately large doses (5 to 10 c.cm.) on three successive days 

 may be given and the animal killed after 7 to 10 days. These methods 

 have the advantage that a precipitating serum is obtained in a short 

 period of time. They do not however yield as strong a precipitating 

 serum as the following slower procedure. One c.cm. of the solution is 

 injected four or five times at intervals of six days. The dosage may 

 also be increased at each successive inoculation, for instance, beginning 

 with 2 c.cm. of an animal serum and increasing gradually through 3, 5 

 and 8 c.cm. to possibly 15 c.cm. at the last injection. The animals 

 should be weighed from time to time and if considerable loss of weight 

 ensues during immunization, the intervals between injections should be 

 increased. 



It is advisable to inject five or six animals at the same time, and by 

 different methods, inasmuch as rabbits vary greatly in their indi- 

 vidual power to produce precipitins and moreover, because some die 

 after the third injection. Frequently only one serviceable serum 

 is obtained, even though the immunization of five rabbits was under- 

 taken. 



Beginning on the sixth day after the last injection, one should, at 

 regular intervals of one or two days, remove a small quantity of blood from 

 the vein of an ear and test the strength of the serum. As soon as' it is 

 found to be satisfactory the animal should be bled and its serum preserved 

 on ice, with precautions for sterility. The rules given above for obtaining 



