BLISTER, a local collection of blood serum beneath the cuticle. Blisters may be produced by a variety of agents. In all in stances, however, there is irritation of the part; this is followed by dilated blood vessels and an exudation of the serum from the blood vessels near the irritant. Medicinally, blistering agents or irritants may be classified in four principal groups, as follows: rubefacients, when redness alone is produced; vesicants, when blistering is brought about; pustulants, when the blisters are usually small and contain pus; and eschar otics, when burning or destruction of tissue may take place. Heat is an excellent illustra tion. Mild heat will cause redness; tempera ture above 125° to F. will cause blister ing; temperature above 400° will burn; and high temperatures can char. The most com monly used blistering agents are heat (the hot iron being lightly touched to the skin), mustard, capsicum, mezereum, turpentine and canthar ides. The hot iron and cantharides are pre ferred, because their action can be controlled. Mustard mixed with cold water makes an ex cellent rubefacient, but it is not advised to be used as a vesicant. Blisters are used to influ ence deep-seated and chronic joint, muscle and tendon troubles. For general purposes of coun ter-irritation rubefacients are more serviceable than vesicants.
or SPANISH FLY, an oil-beetle of the family Meloidcc, in which there is a small head and a distinct neck; the wing-covers and sides of the body are without any coadaptation, while each claw of the feet bears a long appendage closely applied beneath it. The integument is soft, flexible, and many of the species contain a substance which forms an active vesicant, called cantharadine. The Spanish fly (Lytta vesicatoria) is larger than any of our native species, being about an inch long, is of a bright shining green, and when powdered and applied to the skin raises blisters. It inhabits the south of Europe, and is usually imported from Spain. Our native blister-beetles,
when dried, can also be used for producing blisters or making blister-plasters. They are black or gray, and occur on potato plants, on the flowers of the golden-rod, etc. Their trans formations are wonderfully complicated, since they pass through more than one larval stage (see METAMORPHOSIS). The females lay their eggs in the earth; the young, on hatching, are of a primitive shape, called a utri tmgulinn which is very active, entering the egg pods and devouring the eggs of locusts. It soon molts, assuming a different but still active larval stage; it molts again, entering its third larval stage, when it resembles the grub of a May beetle (scarabwid stage). In the fourth stage the grub is helpless, lying on one side; it in creases rapidly in size, and when fully grown leaves the remains of the egg-pod it has been living on and forms a small cavity near by. Here it lies motionless on its side, but gradually contracting till the skin separates and is pushed down to the end of the body, disclosing the semi-pupa or coarctate larva, which hibernates. In the spring the skin bursts and discloses a sixth larval form like the fourth. In this stage it is again active, burrowing in the earth, but taking no food, and in a few days passes into the pupa state. Other species of the family pass through a similar hypermetamorphosis. It is gathered from its food-plants, privet, lilac, etc., at night, by beating the bushes and catching the aroused insects in a cloth. They are then killed by immersing them in hot fluids, usually vinegar and water, are dried and then bottled. Administered internally cantharadine (CoH.0.) causes serious inflammation of the throat, stomach and intestines, and large doses are suffi cient to cause death. Commercially there are various preparations of blister-beetlei, such as cerate of cantharides, tincture of cantharides, plaster of cantharides, etc.