pig was unharmed by an inoculation of half a cubic centimetre (fifteen drops) of a recent virulent culture of diphtheria bacillus if it was injected one hour before with a quantity of serum equal to one fifty-thousandth part of its weight. If this antidiphtheritic serum is mixed with diphtheritic toxine, either in a test-tube or before injection into the organism, the toxine is rendered harmless.
The serum is obtained by abstracting blood from the jugular vein of the horse by means of a small hollow needle. All the instruments employed are carefully sterilized and kept in a five per-cent solution of carbolic acid until they are used. The blood is received in wide-mouthed bottles, holding about two quarts, that have paper tied over the mouths, and that have been carefully sterilized. The horse is blindfolded, its extremities fastened to prevent struggling, a noose is passed around its upper lip, the neck is then made tense, the hair clipped from the skin where the hollow needle is to be introduced, and the entire locality thoroughly scrubbed with a five-per-cent carbolic-acid solution. A small incision is then made through the skin of the neck, and the needle, with the point directed downward, is passed into the jugular vein; a tube connected with the needle is pushed through the paper covering the bottle, and from one and a half to two gallons of blood are withdrawn. The blood is allowed to coagulate and the bottles are placed in an ice chest, where they remain until the serum, amounting to from five to six pints, has separated from the other constituents of the blood. In twenty-four hours, as a rule, the serum is withdrawn from the bottles by means of peculiarly shaped tubes devised by Pasteur, and it is transferred to a flask containing a small piece of camphor that is intended to preserve it.
The serum may be filtered through a porcelain filter if there is reason to believe it was contaminated during its withdrawal, or if it is desired to keep it for some time. As at present prepared the serum has a tendency to lose its remedial influence after it has been kept for a time, and especially if it has been exposed to variations in temperature or to light.
Numerous experiments on animals inoculated with virulent cultures of diphtheria bacilli showed that the quantity of serum necessary to save life varied according to weight, to dose of toxine, to quality of toxine, and to the time of intervention. The serum is preservative and therapeutic, not only when opposed to the toxine but also against the living virus. Roux has frankly acknowledged that these properties of antidiphtheritic serum were discovered by Behring, and upon them depends the serum treatment of diphtheria. The specific action of the serum depends upon a complex substance known as "antitoxine."
