920 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



seems probable that the automatism resides in the muscle tissue. The uterus 

 is, moreover, very sensitive to direct stimulation, even after excision. In ani- 

 mals higher than rabbits a connection with the lumbar spinal cord seems 

 essential to normal labor. Goltz l obtained in dogs conception, pregnancy, and 

 delivery after section of the spinal aord at the height of the first lumbar 

 vertebra. In paraplegic women, with conduction in the cord broken in the 

 dorsal region, delivery is possible. A centre for uterine contraction must 

 hence be supposed to exist in the lumbar cord. Centripetal and centrifugal 

 fibres exist in both sympathetic and spinal nerves, and reflex uterine contrac- 

 tions are readily obtained by stimulation of the central ends of the divided 

 nerve-trunks. According to von Basch and Hofmann, 2 in the dog the sym- 

 pathetic trunks supply the circular muscular coat of the uterine walls and con- 

 tain vaso-constrictor fibres, while the spinal trunks supply the longitudinal 

 coat and contain vaso-dilator fibres. Stimulation of the uterus itself, the 

 vagina, the vulva, the sciatic and the crural nerves, and various sensory 

 regions, notably the nipples, causes reflex contractions of the uterus. The 

 same result occurs upon stimulation of various portions of the brain, such as 

 the medulla oblongata, the cerebellum, the pons, the corpora qtiadrigemina, 

 the optic thalamus, the corpus striatum, and even the corpus callosum. In 

 woman psychic influences may call forth or inhibit uterine contractions. How 

 largely the well-known stimulating effects of the blood in asphyxia and of 

 drugs, like ergot, are due to central, and how largely to direct uterine, influence 

 is undecided. The regular co-ordinated course of labor and many experi- 

 mental facts make it probable that, normally, reflex influences constitute a large 

 part of the process, the centripetal impulses arising within the uterus itself. 

 In fact, it is customary to speak of labor as a complex reflex action. The 

 undoubted automatism of the uterine muscle-fibres must, however, be taken 

 into account, and the act should be regarded as composed of both automatic 

 and reflex elements. We have here to deal with that variety of contractility 

 peculiar to smooth muscle, in which central and peripheral influences work 

 together to bring about the result. It is perhaps not going too far to regard all 

 such actions, like that of the heart, as primarily automatic and called out by 

 direct stimulation, but as modified and controlled by reflex influences. The 

 parturitive contractions of the striated muscles of the abdominal walls are 

 probably more generally reflex in nature, modified, however, by voluntary 

 efforts. 



Multiple Conceptions. According to the records given by different stat- 

 isticians, the frequency of twin births varies considerably in different coun- 

 tries. In 13,000,000 births in Prussia, G. Veit 3 found the number of twins 

 to be 1.12 per cent., or 1 in 89 births. In the cities of New York and 

 Philadelphia recent reports give the ratio of twins to single births as 1 : 120, 

 or 0.83 per cent. 



1 Fr. Goltz : Pftuger's Archivfiir die gesammte Physiologic, ix., 1874. 



2 S. von Basch und E. Hofmann : Medizinische Jahrbilcher, Wien, 1877. 



8 G. Veit: Monatsschrift fur Geburtskunde und Frauenkrankheiten, vi., 1855. 



