1192 



HORMONAL REGULATION 



way rat (Richter and Uhlenhuth, 1954) and 

 mounting behavior in the cow (Gassner, 

 1952), by substances of adrenal cortical 

 origin. The lack of a direct quantitative re- 

 lationship between the components of the 

 total pattern is believed to be accounted for 

 by the existence of different mechanisms, 

 each of which has its own threshold or level 

 of responsiveness to the hormone or combi- 

 nation of hormones for which it is a target 

 organ. Often within individuals this reac- 

 tivity is remarkably constant, for following 

 ovariectomy and replacement therapy with 

 the appropriate hormones, each type of be- 

 havior tends to be displayed in the amount 

 shown before the operation. 



The relationship between estrus and the 

 time of follicular growth and ovulation is 

 summarized in the writer's earlier review 

 (Young, 1941). It is sufficient to note here 

 that in spontaneously ovulating mammals 

 below the primates mating behavior usually 

 is restricted to the hours or days preceding 

 or immediately after ovulation. The occa- 

 sional cow may be an exception. Folley 

 (1952) states: "Provided a cow will stand 

 quietly in stocks, the bull will mount at any 

 time during the oestrous cycle and the cow 

 will allow that." According to Burger (1952), 

 sows not in heat will "ride" proestrous pen- 

 mates. When ovulation is dependent on the 

 stimulus of copulation as in the rabbit, cat, 

 and ferret, indications are that heat does not 

 occur unless large follicles ready for the pre- 

 ovulatory swelling are present (Robinson, 

 1918; Pincus and Enzmann, 1937; Dawson 

 and Friedgood, 1940). In infrahuman pri- 

 mates which have been studied females be- 

 come sexually receptive considerably earlier 

 in the follicular phase than do lower mam- 

 mals and willingness to accept the male is 

 apparent during more of the cycle. Carpenter 

 (1942b) states that free-ranging rhesus mon- 

 keys have a period of receptivity occupying 

 about one-third of the reproductive cycle. 

 The chimpanzee is not greatly different; in 

 adult females the first marked willingness to 

 accept the male coincides with the attain- 

 ment of genital swelling early in the follicu- 

 lar phase (Yerkes and Elder, 1936; Y^oung 

 and Orbison, 1944) . Termination of the pe- 

 riod of receptivity is within 1 or 2 days after 

 ovulation and detumescence on approxi- 



mately day 18 to 20 of the 35- to 37-day 

 cycle (Yerkes and Elder, 1936; Young and 

 Yerkes, 1943) . During the luteal phase there 

 is a general absence of sexual interest 

 (Young and Orbison, 1944) . A diagrammatic 

 representation of the relationships in lower 

 mammals and primates including man is 

 reproduced in Figure 19.1. 



At this point the statement of a concept 

 which has emerged from experimental stud- 

 ies of the guinea pig is appropriate. It ap- 

 plies to the male as well as to the female 

 and is mentioned because it is a part of a 

 thread of thought which has developed Irom 

 the work as a whole rather than from any 

 single facet. The concept is based on the 

 distinction between "responsiveness" and 

 "vigor." It had its genesis in the observa- 

 tions suggesting that differences in the char- 

 acter of the response to gonadal hormones 

 are related to the character of the soma 

 (Young, Dempsey, Myers and Hagquist, 

 1938), but clarification was achieved only 

 after the behavior of female guinea pigs 

 from different genetical strains had been 

 studied (Goy and Young, 1957b). 



Responsiveness in the female is a measure 

 of the effectiveness of a hormone in inducing 

 the estrus characteristics of the individual, 

 but regardless of the character of the estrus 

 relative to that displayed by other animals. 

 Vigor refers to the character of the estrus, 

 i.e., the length of time strong lordoses can 

 be elicited, the duration of the maximal 

 lordosis, and the amount of male-like 

 mounting. Responsiveness in the male is the 

 effectiveness of a hormone in maintaining or 

 restoring the pattern of behavior character- 

 istic of the individual, but regardless of the 

 pattern relative to that seen in other ani- 

 mals. Vigor refers to the character of the be- 

 havior including such measures as length of 

 the interval between the beginning of a test 

 and ejaculation, the number of intromissions 

 preceding ejaculation, and the length of the 

 recovery period following ejaculation. 



It is clear from work with the female ( 1 ) 

 that responsiveness and vigor are influenced 

 by the genetical background (p. 1215), and 

 (2) that they are separable in the sense that 

 a responsive animal may be high or low in 

 vigor and vice versa. Examination of Table 

 VI in the review by Y'oung (1957) reveals 



