PASSIVE IMMUNIZATION 471 



Since the serum is given intravenously it is important to be very 

 careful in estimating whether or not the patient is horse serum sen- 

 sitive. Inquiry as to previous serum injections must be made, and 

 intradermal skin tests with horse serum arc done by injecting, intra- 

 cutaneously, with a tuberculin syringe, a small amount, anywhere 

 from 0.05 to 0.02 c.c. of a 1-10 horse serum dilution. If the injection 

 is properly made, in a sensitive subject within anywhere from five to 

 thirty minutes a large urticaria-like wheal will arise, which will remain 

 for one-half to two hours, gradually disappearing. In such cases great 

 care should be exercised in administering the serum and attempts 

 made at desensitization by the Besredka method, that is, gradual 

 injection of increasing amounts. This is not absolutely reliable, but 

 probably is of great help in most cases. It is best to begin with slow 

 subcutaneous injection of about 0.02 c.c. of horse serum, best diluted 

 in a total quantity of 5 c.c. of salt solution. This can be repeated, 

 gradually increasing the dose to one c.c. in three or four instillations 

 if no untoward symptoms appear. Even in these preliminary injec- 

 tions it is 'best to inject very slowly, and to be sure that the needle does 

 not enter a small venule, leaving about an hour between injections. It 

 is difficult to lay down definite rules for quantity and manner of 

 injection, since in each individual case an experienced worker should 

 feel his way gradually in the case. Gradual desensitization until a 

 large intravenous injection can be given may consume 24 hours or 

 more during which time the cumulative doses may furnish a consider- 

 able fraction of the therapeutic dose. 



When the time for actual injection comes, the serum is diluted 

 with equal parts of sterile salt solution. This permits one to inject 

 the substance more slowly. A special gravity apparatus for slow 

 injection has been devised for this purpose by Cole and his co-workers, 

 but with great care the injection can be done directly with a large 

 syringe. The serum mixture should, of course, be brought to body 

 temperature before injection. The important point is that the injec- 

 tion of the first 10 c.c. of the serum should occupy at least ten minutes, 

 and this is the critical time for the development of anaphylactic symp- 

 toms during which the patient must be carefully watched. Any signs 

 of respiratory difficulty, sudden changes in the pulse, etc., should be 

 an indication for immediate cessation of the injection, which can be 

 begun again when the patient has returned to normal. 



The total dosage advised by Cole and his co-workers is about 90 to 

 100 c.c. Reinjection is a matter of judgment, and these workers advise 



