PRODUCTION AND TESTING OF ANTITOXINS 217 



Park l advises an initial dose of 5,000 toxin units (about 20 c.c. of 

 toxin) combined with 100 units of antitoxin. The same amount is given 

 with the second and third doses of toxin. The intervals are from five 

 days to a week, determined by complete subsidence of the reaction (tem- 

 perature). The doses are increased until, at the end of two or three 

 months, more than ten times the original dose is given (50,000 units). 



Horses vary greatly in the strength of antitoxin which they will pro- 

 duce. At the end of three or four months in favorable animals one 

 cubic centimeter of serum may contain 250 to 800 antitoxin units. Fur- 

 ther immunization will often increase the antitoxin output to 1,000 and 

 more units to the cubic centimeter of serum. Park states that none of 

 the horses used by him has ever yielded 2,000 units to the cubic centi- 

 meter. The same writer advises a three months' period of rest from 

 immunization at the end of every nine months. Given such resting 

 periods, some horses have continued to furnish high-grade antitoxin for 

 from two to four years. 



In order to obtain serum from horses, a sharp cannula is introduced 

 into the jugular vein. After leading the horse into a specially con- 

 structed stall, its head is slightly deflected and pressure is made upon the 

 jugular vein below the point into which the needle is to be plunged. 

 Compression can also be made by surrounding the neck of the horse close 

 to the shoulders with a leather strap over a pad laid directly upon 

 the vein. The vein becomes visible along the lower margin of the neck 

 in a line running from the angle' of the jaw to the edge of the scapula. 

 The skin, of course, is previously shaved and sterilized. The cannula 

 is then plunged into the vein, either with or without previous incision 

 through the skin, and, through a sterile rubber tube, the blood is al- 

 lowed to flow into high glass cylinders or slanted Erlenmeyer flasks. 

 In this way, large quantities of blood may be obtained and, according 

 to Kretz, 2 as much as six liters may be taken at a time at intervals of 

 a month, without injuring the animal. Ligature of the vein after 

 bleeding is unnecessary. 



The cylinders and flasks are allowed to stand for two or three days 

 at or below 10 C. At the end of this time, the serum may be pipetted 

 or siphoned away from the clot and stored in the refrigerator. In order 

 to diminish the chances of contamination, five-tenths per cent of car- 

 bolic acid or four-tenths per cent of tri-cresol may be added. 



1 Park, loc. cit., p. 212. 



2 Kretz', in "Handb. der Techn. u. Meth. d. Immun.," Kraus and Levaditi, vol. ii, 

 1908. 



