They vary in number. Commonly there are from ten to twenty, and it is only in rare cases that less than four or five are found. As soon as they attain the subcutaneous connective tissue they act as foreign bodies, causing a circumscribed inflammation, and finally suppuration. In this way the so-called “warbles” are produced.
Each larva is surrounded by a thick wall, forming a cavity, which communicates with the outer air by a minute aperture.
When the swelling is sufficiently advanced the larva may be extricated by pressing with the fingers around the base of the warble. A few days before it leaves its shelter the larva enlarges the little opening by thrusting its last rings into it. Soon after the larva has escaped the discharge of pus ceases, and the skin wound heals.
Diagnosis. The times at which the swellings appear and the larvæ are present render the diagnosis easy.
Prognosis. This is seldom grave, for the larvæ rarely cause death. In cases where they are present in very large numbers, however, they may set up purulent infection.
Treatment. No really effective treatment against warbles is known. Curative treatment consists in squeezing out or killing the larvæ when in the subcutaneous tissue, but this is practically useless, as the dead larvæ then set up prolonged suppuration.
CHAPTER III.
RINGWORM.
The old term “ringworm” is still used to indicate a well-marked skin disease due to parasitic fungi which grow at the expense of the epidermis. Other names, such as dermatophytis and epidermophytis, have been suggested, to indicate the mode in which the parasite grows. The term dermatomycosis suggests a cutaneous vegetable parasite.
The dermatomycoses of the domestic animals are caused by fungi belonging to six distinct genera:—
Trichophyton (horse, ass, ox, dog, pig); Eidamella (dog); Microsporum (horse, dog); Achorion (dog); Lophophyton (fowl); Oospora (dog).