Antidiphtheric Serum is derived from the blood of a horse in which high immunity has been produced by a succession of gradually increasing doses of diphtheria toxin. This immunity is the result of the development of some substance termed antitoxin.

The antitoxins are efficient through neutralization of the toxins generated by the diphtheria bacilli. The serum produces no symptoms due to the antitoxin; but erythemas, fever and fleeting pains sometimes occur as a result of inevitably-retained anaphylactic substances.

Therapeutics. - The serum is specific in diphtheria if used early, and in sufficient amount.

Dose. - Prophylactic, 1ooo units; combative, 10,000 units, repeated.

(A unit is the amount necessary to protect a 250-Gm. guinea-pig against 100 times the fatal dose of toxin.)

Antitetanus Serum is derived from immunized horse serum. It is used to counteract the toxin of tetanus, and seems to act more efficiently as a preventive than as a curative.

Dose. - One thousand units; repeated as necessary.

Typhoid Vaccine has given remarkable results in the army as a preventive of enteric fever.