Before inserting the speculum, however, the genital passages should be cleaned, and the speculum itself smeared with vaseline. It penetrates readily with moderate pressure.
Heifers and similar animals require a special (small) instrument (Fig. 318).
Fig. 318.—Vaginal speculum for heifers.
In certain circumstances, moreover, it is preferable to use retractors, with which local examination is easier. These can be applied at either side of the vagina and drawn apart, thus exposing the depths of the genital tract.
CASTRATION OF THE COW.
The operation of castrating the cow is very old, and was mentioned by both Aristotle and Pliny. Many other descriptions of it have since been given. But more recently the manual technique has been considerably simplified and very fully described.
Utility.—The operation is practised for the cure of nympho-mania; also to prolong the period of milk-yielding and to facilitate fattening.
As regards nympho-mania, it is only of value where the excessive excitement is due to disease of the ovaries.
Under ordinary conditions the secretion of milk diminishes more or less, and becomes very slight after eight or nine months from calving. If, however, the cow is castrated under favourable circumstances, lactation continues for several months, sometimes for several years, beyond this period. It is said that castrated cows yield milk of a more constant composition and richer in butter fat, casein, and mineral salts than those which are not castrated, although the point cannot be said to have been fully established.