982 OP GENERATION. 



full term of development (as in cases of superfcetation, 990) the other, if its 

 development at this period is far from complete, is often retained, and goes on 

 to its full term, its placenta not being detached in the first parturient effort, 

 because it was not then prepared for the separation. It is obvious that this 

 view affords a rational explanation of the occurrence of uterine action in cases 

 of extra-uterine foetation; for, if the condition of the placental attachment 

 furnish its exciting cause, it will do so equally, whether the placenta be 

 attached to the lining of the uterus, or to that of the Fallopian tube, or to any 

 other organ. It is an additional indication that the immediate stimulus to the 

 parturient effort of the uterus is given by some change in the condition of its 

 foetal connections, that the term of gestation seems capable of being prolonged 

 by peculiarities in the constitution or rate of development of the foetus, which 

 are derived from the male parent ; for it was ascertained by the late Earl Spen- 

 cer, 1 that of 75 cows in calf by a particular bull, the average period was 288 J 

 days, instead of 280 ; none of these having gone less than 281 days, and two- 

 fifths of them having exceeded 289 days. 2 



988. Although the duration of Pregnancy is commonly stated at nine solar 

 months, it would be more correct to fix the period at 40 weeks, or 280 days ; 

 which exceeds nine calendar months by from 5 to 7 days, according to the 

 months included. 3 This, at least, is the average result of observation, in cases 

 in which the period of Conception could be fixed, from peculiar circumstances, 

 with something like certainty ; but there can be no doubt that variations of a 

 few days, more or less, are of continual occurrence. The period of Quickening 

 may be relied on in some women, in whom it occurs with great regularity in a 

 certain week of Pregnancy; but in general there is great latitude as to the time 

 of its occurrence. The usual or average time is probably about the 18th week. 



989. The question of the extreme limit of Gestation is one of great import- 

 ance both to the Practitioner and to the Medical Jurist ; but it is one which 

 cannot yet be regarded as satisfactorily decided. Many persons, whose expe- 

 rience should give much weight to their opinion, maintain that the regular 

 period of 40 weeks is never extended for more than two or three days ; whilst, 



1 See Dr. J. C. Hall in "Medical Gazette," May 6, 1842. 



2 The very ingenious doctrine has been propounded by Dr. Tyler Smith ("Parturition, 

 and the Principles and Practice of Obstetrics," London, 1849), that the exciting cause of 

 parturition is to be found in the recurrence of the periodical excitement of the ovary, act- 

 ing by reflection on the uterus through the spinal system of nerves, the ovarian nerves 

 being the exciters and the uterine the motors; this excitement continuing during the entire 

 period of gestation, and giving a special tendency to abortion at each return ; and acting 

 with such potency at the eleventh recurrence as then to induce the parturient effort. He 

 assigns no other cause, however, why this eleventh recurrence should be so much more 

 effectual than the rest, than that by this time there is a much greater aptitude to con- 

 traction in the uterus itself, and an increased readiness to be thrown off on the part of the 

 placenta conditions which seem to the Author to be in themselves adequate to account 

 for the result. Dr. Tyler Smith's hypothesis is distinctly negatived by the following facts: 

 1. The period of gestation, although commonly a multiple of the menstrual interval, is by 

 no means constantly so ; the former remaining normal when the latter is shorter or longer 

 than usual. 2. Parturient efforts take place in the uterus, notwithstanding the previous 

 removal of the lower part of the spinal cord. 3. The removal of the ovaries in the later 

 part of gestation does not interpose the least check to the parturient action, as Prof. 

 Simpson, of Edinburgh, has experimentally ascertained. The Author considers himself 

 fully justified, therefore, in asserting that this hypothesis does not possess the slightest 

 claim even to be entertained as a possible one ; and would refer, for a more detailed exami- 

 nation of it, to the "Brit, and For. Med.-Chir. Review," vol. iv. p. 1. 



3 The mode of reckoning customary among women, is to date from the middle of the 

 month after the last appearance of the Catamenia ; but it is certain that Conception is 

 much more likely to take place soon after they have ceased to flow, or even just before 

 their access, than in the intervening period ($ 966) ; so that, in most instances, it would 

 be most correct to expect labor at forty weeks and a few days after the last recurrence of 

 the Menses. 



