(ESTRUM. 



59 



time towards the end of spring, in order to have two litters within the 

 twelvemonth. 



The frequency and duration of the period of " rutting " or "heat " depends 

 upon the age, species, and other circumstances ; but it may be said to 

 persist in the domesticated animals from one to fifteen days at the most. 

 The shortest period is witnessed in the Cow and Sheep, and the longest 

 in the Bitch. It is sometimes only present from twelve to twenty-four 

 hours in some non-fecundated animals. With impregnation, however, it 

 ordinarily ceases until after parturition ; and if impregnation does not 

 occur, it gradually disappears until the next period, which is somewhat 

 variable. Its re-appearance in the Cow has been noted every month or 

 three weeks, and sometimes at closer intervals ; and in the Sheep and Pig 

 it lasts for one or two days, and again appears from the fifteenth to the 

 thirtieth day, but usually every month. When removed from artificial con- 

 ditions, it is stated that the ovine species is in rut in September, that this 

 persists only for a day, but re-appears every fourteen days until the end 

 of December. From the spring until the end of summer, it may be said 

 the Mare manifests a desire for the Horse every three or four weeks, and 

 the objective phenomena which announce it continue from two to four 

 days. In the Bitch they last for nine or ten days, and, as has been stated, 

 dnly appear in the spring and autumn. 



This periodicity is regulated by Nature, with a view to the preservation 

 of species ; and in animals not influenced by artificial conditions, it is so 

 arranged that the young creatures may arrive during the season when their 

 maintenance will be best assured. 



With the subsidence of venereal excitement in unimpregnated animals, 

 there succeeds a period of calm, which is almost equivalent to that of ges- 

 tation in impregnated creatures. And, strange to say, with Bitches at the 

 end of this interval — from the fortieth to the sixtieth day — there some- 

 times appear phenomena allied to the parturient period : as tumefaction 

 of the mammary glands, followed by swelling and increase of the opening 

 of the vulva, with reddening of the vaginal mucous membrane and the es- 

 cape of a viscid fluid. The animal also acts as if about to bring forth : 

 making a bed for her young ; moving about uneasily ; neglecting her food 

 for three or four days, during which the mammae become still more devel- 

 oped, firm, and elastic, the teats elongated, and the lactiferous sinuses 

 filled with an abundance of good milk, which is easily obtained by slight 

 pressure. If a Bitch in this state is presented with a young puppy, she 

 will take to it as if it were her own, and rear it most affectionately. This 

 strange condition has been observed, though more rarely, in the Cat ; and 

 Chauveau has also noticed it in a Mare which had been put to the Horse, 

 but did not prove in foal. 



The years during which oestrum continues varies with species, and par- 

 ticularly with regard to the age they attain ; but it always disappears to- 

 wards the decline of life. 



Climate, inseparable from the conditions of alimentation, exercises a 

 marked influence on the "rut," in hastening its development and its period- 

 icity ; but the economical law to which it is subordinate does not vary. 

 With many species, the rut only appears once a year ; while in others which 

 are favorably placed with regard to alimentation, it persists in every sea- 

 son, or at least during a large part of the year. Domesticity, in assuring 

 animals food and shelter, and removing them from the risks and alterna- 

 tions of an erratic life, multiplies the periodical returns of this condition. 



