i88 INTERNAL SECRETIONS OF THE OVARY 



described for both the rat (87) and the mouse (501). In the 

 mouse the injection of the sodium hydroxide extract of anterior 

 pituitary made possible the production of deciduomata in the 

 unmated animal, but not in the unmated sterilized mouse in 

 spite of the conversion of the irradiated ovary into luteal tissue. 

 The nature of the activity by which the corpus luteum sensi- 

 tizes the uterine mucosa is just beginning to be understood. 

 Loeb (383) originally reported two interesting facts, {a) that the 

 sensitization is specific to the uterus, other tissues not being 

 affected, (b) that the sensitization is equally well induced in 

 grafted uterine tissue. These observations made it clear that 

 the sensitization is chemical in nature, but initial attempts at 

 preparing from the corpus luteum an extract capable of causing 

 this sensitivity, when it would otherwise be absent, were not 

 successful. Loeb (383) obtained only negative results from the 

 injection into ovariectomized animals of corpora lutea extracts 

 and also by the injection of blood from animals in the stage of 

 uterine sensitivity. These results, however, were merely incon- 

 clusive. Recently Weichert (633) has been successful in sensi- 

 tizing the uterus of the rat during the unmated dioestrous cycle 

 by the injection of the oestrus-inhibiting extract of corpus 

 luteum as prepared by Hisaw and his co-workers. A similar 

 result followed injection of corpus luteum extract in the ovariec- 

 tomized animal, provided that an artificial oestrous period had 

 been first induced by the injection of the oestrus-producing 

 hormone. This work of Weichert is of extraordinary interest in 

 showing that the preliminary activity of the oestrus-producing 

 hormone may be necessary for the later action of the corpus 

 luteum secretion. 



(d) DEVELOPMENT OF THE MAMMARY GLANDS 



The facts which have been recorded in previous chapters make 

 it clear that two stages of development take place in the 

 mammary glands even before the appearance of the first corpus 

 luteum. These two stages are (a) a slight pre-pubertal develop- 

 ment from the time when the female mammary gland differen- 

 tiates from its male analogue, and (b) a burst of growth at the 

 first and subsequent oestrous periods (see p. 130). This growth 



