916 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Other organic changes are, however, more profound than these mechanical ones. 

 In accordance with the increased nutritive labor thrown upon the mother, the 

 total quantity of blood in her body is increased, if we can reason from deter- 

 minations made upon the lower animals. 1 The condition of the blood is dis- 

 puted. The old view was that the blood of pregnancy is more watery and 

 contains less hemoglobin than at other times. This is perhaps true for the 

 earlier months, but Schroeder 2 and others have shown that the proportion of 

 haemoglobin and the number of red corpuscles rise above the normal during 

 the later stages. The work of the maternal heart is increased during gestation. 

 It is maintained by some that the heart beats more rapidly according to 

 Kehrer, 3 over eighty in the minute. It has al.4o been thought, mainly from 

 the results of percussion and from sphygmographic tracings, that the left ven- 

 tricle is hypertrophied during pregnancy. Post-mortem examination, although 

 scanty, cannot be said to confirm this inference. Pregnancy necessarily throws 

 increased labor upon both the liver and the kidneys, and these organs are prone 

 to functional disorders. Gastric disturbances are marked by frequent vomit- 

 ing. A tendency to increased pigmentation in the skin is present. The ner- 

 vous system is affected, manifesting its alterations both by nutritional disturb- 

 ances and by mental irritability, depression of spirits, disordered senses, easily 

 passing into temporary pathological states, and occasionally by feelings of 

 heightened well-being. The body-weight usually increases independently of 

 the added weight of the embryo. 



Duration of Gestation. For centuries the duration of gestation in 

 woman has been commonly regarded as 280 days. The beginning of preg- 

 nancy, the union of the ovum and the spermatozoon, however, presents no 

 obvious signs by which it may be recognized, and hence the actual length of 

 pregnancy in the human female is no more known than in other mammals. 

 The obstetrician is obliged, therefore, to use artificial schemes in computing its 

 probable length. Several tables have been published of the time elapsing 

 between a single coition resulting in pregnancy and the terminal parturition. 

 Veit, 4 in collecting 503 such cases reported by several obstetricians, finds the 

 duration to be from 265 to 280 days in 396 cases, and longer in the remaining 

 107 cases, the variation thus being marked. It is obvious that the date of the 

 effective coition can rarely be known. One of the first and most evident signs 

 of pregnancy is the non-appearance of the menses, and, probably largely from 

 the long-prevailing idea of the close relation existing between ovulation and 

 menstruation, it has been customary to regard gestation as dating from the last 

 menstruation. Following Naegele, obstetricians estimate the date of parturi- 

 tion as 280 days from the first day of the last menstruation ; and this simple 

 but artificial rule is doubtless approximately correct. 



In accordance with modern biological theories, it must be supposed that for 



1 O. Spiegelberg und R. Gscheidelen: Archivfur Gyndkologie, iv., 1872. 



2 B. Schroeder : Archivfiir Gynakoloyie, xxxix., 1890-91. 



3 F. A. Kehrer : Ueber die Veranderungen der Pulscurve im Puerperium, 1886. 



4 J. Veit: Miiller's Handbuch der Oeburtshillfe, 1, 1888. 



