By far the most used of the antitoxin sera is the Serum Antidiphtheriticum of the United States Pharmacopoeia. This serum is sold in sealed packages bearing a definite date, later than which the contents of the package should not be used on account of the possibility of its deterioration. The number of antitoxin units which each package represents is printed upon the package. Antitoxin is now furnished in an hermetically sealed syringe, and the package contains full instructions how to use each particular maker's product.

Antitoxin is always given hypodermatically, and the site of injection is a matter of choice, perhaps the best place being in the abdominal wall or in the suba.xillary region. As the bulk of the injection is considerably more than the content of an ordinary hypodermic syringe, injection should be made between the skin and muscle-fascia, i. e., in the loose subcutaneous tissue, so that distention will not cause pain. Strict asepsis should be used in preparing the region for the injection, and the serum should he injected slowly, care being taken to avoid the blood vessels. When the needle is withdrawn use gentle pressure for a moment at the point of puncture with sterile gauze or cotton, and then seal with collodion or a small strip of adhesive plaster.