98 INTERNAL SECRETIONS OF THE OVARY 



described a decrease of the chromatophil cells of the cervical 

 ganglion of the mouse after castration. They found that such 

 cells amounted to 2-5^0 in the normal animal, i-o°q after 

 castration, and 15 '-^ during pregnancy. Since the injection of 

 oestrin into the ovariectomized animal raised the percentage, 

 they suggest this as a possible test for the hormone. It is 

 obvious, however, that no technique for the assay of oestrus- 

 producing activity has the ease and reliability of the vaginal 

 smear, and, provided that all anomalous results, such as the 

 extraction of oestrus-producing substances from male urine and 

 plants, are checked by means of other criteria, the vaginal 

 smear technique is probably adequate. 



Ovarian regeneration. The basis of the assay of ovarian 

 extracts at the present moment is the absence of the ovaries, and 

 it is thus necessary to consider the possibility of the appear- 

 ance of ovarian tissue in ovariectomized animals. Such tissue 

 may occur in one or both of two ways: 



[a) A small percentage of animals have accessory ovaries 



which may escape removal at the time of ovariectomy 



(see p. 12). 

 {h) Even after the complete removal of all ovarian tissue at 



the time of operation, new ovarian tissue may 



regenerate. 



As regards accessory ovaries, it is safe to say that their occur- 

 rence is rare (p. 12). In any case, the presence of ovarian 

 tissue, apart from the two normal ovaries, would presumably 

 result in the continuation of the cycle after double ovariectomy, 

 and this would indicate at once, either that the two normal 

 ovaries had not been completely removed, or else that accessory 

 tissue was present. The regeneration of ovarian tissue presents, 

 however, a more difficult problem. This phenomenon was noted 

 by Castle and Phillips (116) in the guinea-pig. These authors 

 reported ten cases of regeneration after ovariectomy of 74 

 guinea-pigs and 17 rabbits. In three of these animals, litters 

 were produced after ovariectomy. Subsequently the same 

 authors reported eleven regenerations in 141 ovariectomized 

 guinea-pigs. In these cases, however, no criteria of complete 

 initial removal appear to have been available. In view of the 



