5i8 THE POPULAR SCIENCE MONTHLY. 



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 antidiphthe- 

 ritic serum is mixed with diphtheritic toxine, either in a test-tube 

 or before injection into the organism, the toxine is rendered harm- 

 less. 



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 care- 

 fully 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 thor- 

 oughly 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 jugu- 

 lar 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 of blood are withdrawn.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 rule, the serum is withdrawn from the bottles by means of pecul- 

 iarly shaped tubes devised by Pasteur, and it is transferred to a 

 flask containing a small piece of camphor that is intended to pre- 

 serve 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 pre- 

 pared 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 op- 

 posed 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." 



