Sexual Cycle 



445 



by acute circulatory disturbances and by secondary destructive 

 effects of leucocytes. 



We would conclude on the basis of the observations of Long 

 and Evans in the rat that in this species the sexual cycle consists 

 essentially only of the first phase and of the intermission; the 

 lutein phase is here lacking under ordinary conditions, but can 

 be called forth experimentally and is present also during lac- 

 tation. We would interpret in a similar way the observations 

 of Allen in the mouse. 



The specific relation of these growth substances to certain 

 tissues is very pronounced. The corpus luteum substance of the 

 guinea pig acts very strongly on the connective tissue of the 

 uterus, but not at all on that of the vagina ; the follicular substance 

 acts on the vagina and on the uterus in a manner quite different 

 from the corpus luteum substance. This specificity is due to the 

 character of these growth substances as well as of the tissues on 

 which they act, and not to the position of the tissues of the body. 

 It can be shown that this specificity is still noticeable in uterine 

 tissue after it has been transplanted subcutaneously. 



On the basis of these observations we would propose the fol- 

 lowing classification of the periods of the sexual cycle. In the 

 various species individual differences exist; thus in the rat and 

 mouse only phases I and II can be recognized. 



I. Follicular phase — 



a. Proceestrus. 



b. Oestrus. 



c. Metoestrus (in some cases). 



II. Intermediate phase (following ovulation and preceding 

 sentization of the uterus). 



III. Lutein phases— 



a. Period of sensitization of uterus. 



b. Period of return to the resting state. 



c. Period of resting state. 



