458 HORSE, SWINE AND POULTRY DISEASES 



septic solution before each bleeding. The blood is immediately taken 

 to the laboratory and defibrinated, leaving only the fluid part of the 

 blood, which we call the serum. To this serum is added a small 

 amount of a weak solution of carbolic acid to partially preserve it. 

 It is then stored in a cool place until tested on some pigs, when, if 

 it proves potent, it is ready for use. 



Before the hog is ready to be bled for this serum it must first 

 undergo the process of hyperimmunization that is, his blood must 

 be brought into a condition so that when it is drawn and injected into 

 other hogs it will prevent them from taking the cholera. For this- 

 process one is taken which is immune to cholera that is, it has 

 either recovered from a case of cholera or has been vaccinated against 

 the disease, and will therefore not take the disease again. Into this 

 animal is injected, through the veins of the ear usually, five cubic 

 centimeters of virulent blood for each pound of weight of the hog; 

 for instance, a 200-pound hog receives 1,000 cc. of virulent blood. 

 After ten days the hog is ready to produce blood for serum and is 

 bled usually three times more at intervals of seven days, and if the 

 tail holds out he is then rehyperimmunized and again bled two or 

 three times, the same as before. In either case at the last bleeding 

 the hog is killed and all of his blood taken. The serum from all of 

 these drawings is mixed together and its potency tested. If it is po- 

 tent, it is ready for use. This is necessary as the serum from the last 

 drawing is usually less potent than that from the first drawings, and 

 after it is all mixed together it should be a serum of average potency. 



The amount of serum produced from each drawing varies with 

 the size of the hog, with his condition, the character of the weather 

 and the manner in which the animal has been fed and cared for. A 

 200-pound hog will produce usually 600 cc. of serum at each bleed- 

 in-g, or a total of 3,000 cc. the last bleeding when killed usually 

 yields 1,200 cc. of serum. 



It takes much practice and patience to inject such a large quan- 

 tity of blood into the ear vein and also to draw such a large quantity 

 from the tail of the hog. All of these operations must be done with 

 thoroughly antiseptic precautions, to produce potent serum and to 

 prevent injury to the pig itself or accidents to the serum. 



To produce virulent blood enough to hyperimmunize a 200- 

 pound hog requires three or four pigs weighing about forty pounds. 

 They must be given a severe form of the disease and must be ready 

 to kill at, or near, a certain time, as the virulent blood must be used 

 for this work within a few hours after drawing. Again, in testing 

 the serum it is necessary to use several more pigs. These are not all 

 a total loss as it is usually possible to save their blood by killing them 

 when they are about to die with the disease. Here again is the knowl- 

 edge of the expert required. If the pig is killed too soon, the blood is 

 not virulent enough for use, and if allowed to go too long before kill- 

 ing, the pig is liable to die and the blood cannot then be used at all. 

 In order to produce this 3,000 cc. of serum it requires one 200-pound 

 hog and about five smaller pigs. This amount of serum will vacci- 



