230 ANTITOXINS 



the temperature reaction has subsided, a second subcutaneous injection 

 of a slightly larger dose is given, the amount of toxin increasing about 

 10 to 15 c.c. per dose, until, six weeks later, the animal is receiving from 

 20 to 30 times the amount originally given. At the end of this time a 

 trial bleeding is made and the serum tested. 



There is absolutely no way of judging which horses will produce the 

 highest grades of antitoxin. Roughly estimated, those horses that are 

 extremely sensitive and those that react feebly are the poorest, but 

 there are exceptions even in these cases. The only reliable method, 

 therefore, is to bleed the horses at the end of six weeks or two months 

 and test their serum. If only high-grade serum is wanted, all horses 

 that give less than 150 units per cubic centimeter should be discarded. 

 The remaining horses should receive steadily increasing doses, the 

 rapidity of the increase and the interval of time between the doses 

 (three days to one week) depending somewhat on the reaction following 

 the injection, an elevation of temperature of more than 3 F. being un- 

 desirable. 



For example, according to Park, a horse that yielded an unusually 

 high grade of serum was started on 12 c.c. of toxin (-j-g-g- c.c. fatal dose), 

 together with 10,000 units of antitoxin. Sixty days later a dose of 675 

 c.c. was given, and the serum contained 1000 units of antitoxin per 

 cubic centimeter. Regular bleedings were made weekly for the next 

 four months, at the end of which time the serum had fallen to 500 units 

 in spite of weekly gradually increasing doses of toxin. At the end of 

 three months the antitoxic serum of all the horses should contain over 

 300 units, and in about 10 per cent, as much as 800 units in each cubic 

 centimeter. Not more than 1 per cent, give above 1000 units, and, 

 according to Park, so far none has given him as much as 2000 units per 

 cubic centimeter. The very best horses, if pushed to their limit, con- 

 tinue to furnish blood containing the maximum amount of antitoxin 

 for several months, and then, in spite of increasing injections of toxin, 

 begin to furnish blood of gradually decreasing strength. If an interval 

 of three months' freedom from inoculation is allowed once every nine 

 months, the best horses will furnish high-grade serum for from two to 

 four years. 



Collecting the Serum. In order to obtain the serum, the neck of 

 the horse should be cleansed thoroughly as for an aseptic operation, and 

 a special tourniquet applied to distend the jugular vein. A small slit 

 is made through the skin over the vein, and a special sharp-pointed 

 cannula is passed upward under the skin for two inches or more and 



