A polyvalent serum, that is, one derived from an animal which has been immunised by numerous strains of the organism derived from various sources, is much more efficacious than when a single strain has been used.

Clinical Use of Serums.—­Every precaution must be taken to prevent organismal contamination of the serum or of the apparatus by means of which it is injected.  Syringes are so made that they can be sterilised by boiling.  The best situations for injection are under the skin of the abdomen, the thorax, or the buttock, and the skin should be purified at the seat of puncture.  If the bulk of the full dose is large, it should be divided and injected into different parts of the body, not more than 20 c.c. being injected at one place.  The serum may be introduced directly into a vein, or into the spinal canal, e.g. anti-tetanic serum.  The immunity produced by injections of antitoxic sera lasts only for a comparatively short time, seldom longer than a few weeks.

"Serum Disease” and Anaphylaxis.—­It is to be borne in mind that some patients exhibit a supersensitiveness with regard to protective sera, an injection being followed in a few days by the appearance of an urticarial or erythematous rash, pain and swelling of the joints, and a variable degree of fever.  These symptoms, to which the name serum disease is applied, usually disappear in the course of a few days.

The term anaphylaxis is applied to an allied condition of supersensitiveness which appears to be induced by the injection of certain substances, including toxins and sera, that are capable of acting as antigens.  When a second injection is given after an interval of some days, if anaphylaxis has been established by the first dose, the patient suddenly manifests toxic symptoms of the nature of profound shock which may even prove fatal.  The conditions which render a person liable to develop anaphylaxis and the mechanism by which it is established are as yet imperfectly understood.

Vaccine Treatment.—­The vaccine treatment elaborated by A. E. Wright consists in injecting, while the disease is still active, specially prepared dead cultures of the causative organisms, and is based on the fact that these “vaccines” render the bacteria in the tissues less able to resist the attacks of the phagocytes.  The method is most successful when the vaccine is prepared from organisms isolated from the patient himself, autogenous vaccine, but when this is impracticable, or takes a considerable time, laboratory-prepared polyvalent stock vaccines may be used.