270 INFECTION AND IMMUNITY 



by chemicals or heat, or combined with antitoxin. In the Pasteur 

 Institute in Paris, the small initial dose of toxin (0.5 c.c.) is mixed 

 before injection with an equal quantity of Lugol's solution (iodiii- 

 potassium iodid solution). 



Park 3 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 (temperature). 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 

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

 one cubic centimeter of serum may contain 250 to 800 antitoxin 

 units. Further immunization will often increase the antitoxin out- 

 put 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 centimeter. 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 in- 

 troduced into the jugular vein. After leading the horse into a 

 specially constructed 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 allowed to flow into high 

 class cylinders or slanted Erlenmeyer flasks. In this way, large 

 quantities of blood may be obtained and, according to Kretz, 4 as 

 much as six liters may be taken at a time at intervals of a month, 



'Park, loc. cit., p. 212. 



4 Kretz, in "Handb. der Techn. u. Meth. d. Immun., " Kraus and Levaditi, 

 vol. ii, 1908. 



