608 OF REPRODUCTION. 



of Tessier, which were continued during a period of forty years, with every 

 precaution against inaccuracy, have furnished a body of results which seems 

 quite decisive. In the Cow, the ordinary period of gestation is about the same 

 as in the Human female ; but out of 577 individuals, no less than 20 calved 

 beyond the 298th day, and of these, some went on to the 321st, making an 

 excess of nearly six weeks. Of 447 Mares, whose natural period of gesta- 

 tion is about 335 days, 42 foaled between the 359th and the 419th day, the 

 greatest protraction being thus 84 days, or just one-fourth of the usual term. 

 Of 912 Sheep, whose natural period is about 151 days, 96 yeaned beyond the 

 153d day ; and of these, 7 went on until the 157th day, making an excess of 

 6 days. Of 161 Rabbits, whose natural period is about 30 days, no fewer than 

 25 littered between the 32d and 35th ; the greatest protraction was here one- 

 sixth of the whole period, and the proportion in which there was a manifest 

 prolongation was also nearly one-sixth of the total number of individuals. In 

 the Incubation of the common Hen, Tessier found that there was not unfre- 

 quently a prolongation to the amount of 3 days, or one-seventh of the whole 

 period. In regard to Cows, the observations of Tessier have been recently 

 confirmed by those of Earl Spencer, who has published* a table of the period 

 of gestation as observed in 764 individuals ; he considers the average period 

 to be 284 or 285 days : but no fewer than 310 calved after the 285th day ; 

 arid of these, 3 went on to the 306th day, and 1 to the 313th. It is curious 

 that, among the calves born between the 290th and 300th days, there was a 

 decided preponderance of males, these being 74, to 32 females ; whilst all of 

 those born after the 300th day were females.! These variations are probably 

 to be regarded as due, not so much to a prolongation of the period of Utero- 

 gestation, as to various circumstances which may have a retarding influence 

 on the process of Fecundation, and on the transmission of the Ovum through 

 the Fallopian tube. These have been well pointed out by Dr. Montgomery.^ 

 It may be added that, in Dr. Barry's observations on the early changes that 

 take place in the Ovum of Rabbits, he has noticed several irregularities of this 

 description.* On the whole, it may be considered that in regard to the Human 

 female, the French law is a very reasonable one. It is probable, from the cir- 

 cumstances alluded to in the preceding paragraph, that Gestation is protracted 

 to the extent of a week, ten days, or a fortnight, much more frequently than 

 is commonly supposed. In several of the cases in which the protraction ap- 

 peared indubitable, the Infant was unusually large and vigorous. 



756. In regard to the shortest period at which Gestation may terminate, 

 consistently with the viability of the Child, there is a still greater degree of 

 uncertainty. Most practitioners are of opinion, that it is next to impossible 

 for a Child to live and grow to maturity, which has not almost completed its 

 seventh month ; but it is almost unquestionable that Infants which have been 

 born at a much earlier period, have lived for some months. It is rare in such 

 cases, however, that the date of Conception can be fixed with sufficient pre- 

 cision, to enable a definite statement to be given. Of the importance of the 

 question, a case which recently occurred in Scotland afFords sufficient proof. 



* Journal of the English Agricultural Society, 1839. 



f It appears, however, from some recent statements published on the authority of Earl 

 Spencer, that the Male may exert an important influence on the period of gestation. Of 

 75 Cows in calf by a particular bull, the average period was 2884 days, or four days 

 more than the usual period. Of the 764 cows previously mentioned, 185 (nearly one- 

 fourth) went less than 281 days; whilst not one of the cows in calf to this bull did so. 

 On the other hand, of the 764 cows first mentioned, 111 (rather more than one-seventh) 

 went above 289 days; while by this bull 29 out of 75 (nearly two-fifths) went above 289 

 days. Dr. J. C. Hall, in Medical Gazette, May 6, 1842. 



t Op. cit., p. 272. 



