Their size varies as the skin is more or less folded or stretched, while we have supposed in the figures that the skin is uniform or free from folds, but not stretched out. In order to understand the differences which the milk-mirrors present in respect to size, according to the state of the skin, the milk-mirror is shown in two ways in [Figs. 52] and [53]. In [Fig. 53] the proportions are preserved the same as in the other mirrors represented, but an effort is made to represent the folds of the skin; while in [Fig. 52] the mirror is just as it would have been had the folds of the udder been smoothed out, and the skin between the udder and the thighs stretched out; or, in other words, as if the skin, covered with up-growing hair, had been fully extended.
This mirror, but little developed, just as shown in [Fig. 53], was observed on a very large Norman cow.
It is usually very easy to distinguish the milk-mirrors by the upward direction of the hair which forms them. They are sometimes marked by a line of bristly hair growing in the opposite direction, which surrounds them, forming a sort of outline by the upward and downward growing hair. Yet, when the hair is very fine and short, mixed with longer hairs, and the skin much folded, and the udder voluminous and pressed by the thighs, it is necessary, in order to distinguish the part enclosed between the udder and the legs, and examine the full size of the mirrors, to observe them attentively, and to place the legs wide apart, and to smooth out the skin, in order to avoid the folds.
The mirrors may also be observed by holding the back of the hand against the perineum, and drawing it from above downwards, when the nails rubbing against the up-growing hair, make the parts covered by it very perceptible.
As the hair of the milk-mirror has not the same direction as the hair which surrounds it, it may often be distinguished by a difference in the shade reflected by it. It is then sufficient to place it properly to the light to see the difference in shade, and to make out the part covered by the upward-growing hair. Most frequently, however, the hair of the milk-mirror is thin and fine, and the color of the skin can easily be seen. If we trust alone to the eye, we shall often be deceived. Thus, in [Figs. 52] and [53], the shaded part, which extends from the vulva to the mirror E, represents a strip of hair of a brownish tint, which covered the perineum, and which might easily have been taken for a part of the milk-mirror.
In some countries cattle-dealers shave the back part of the cows. Just after this operation the mirrors can neither be seen nor felt; but this inconvenience ceases in a few days. It may be added that the shaving, designed, as the dealers say, to beautify the cow, is generally intended simply to destroy the milk-mirror, and to deprive buyers of one means of judging of the milking qualities of the cows.
It is not necessary to add that the cows most carefully shaven are those which are badly marked, and that it is prudent to take it for granted that cows so shorn are bad milkers.
Milk-mirrors vary in position, extent, and the figure they represent. They may be divided, according to their position, into mirrors or escutcheons, properly so called, or into lower and upper tufts, or escutcheons. The latter are very small in comparison with the former, and are situated in close proximity to the vulva, as seen at S in [Figs. 38], [39], [40], etc. They are very common on cows of bad milking races, but are very rarely seen on the best milch cows. They consist of one or two ovals, or small bands of up-growing hair, and serve to indicate the continuance of the flow of milk. The period is short in proportion as the tufts are large. They must not be confounded with the escutcheon proper, which is often extended up to the vulva. They are separated from it by bands of hair, more or less large, as in [Figs. 40], [42], &c.
The mirrors shown in [Figs. 38] to [42], and [29] to [35], &c., exist, more or less developed, on nearly all cows, and indicate the quantity of milk, which will be in proportion to their size. Sometimes they form only a small plate on the posterior surface of the udder, as in [Fig. 49]. In other cases they cover the udder, the inner surface of the legs and the thighs, the perineum, and a part of the buttocks, as in [Figs. 29], [30], [31], &c.
Two parts may be distinguished in the lower tufts: one situated on the udder, the legs, and the thighs, as at M M, [Fig. 30]; and the other on the perineum, extending sometimes more or less out upon the thighs, as at P P, in the same figure.