1890.] The Sympathetic Nervous System in Mammals. 19 



auscultation. If telephone and stethoscope nre applied to the same 

 ear, one sound only is heard. Exner has shown that any two sounds 

 which are as much as -5^ of a second apart are audible as distinct 

 sounds. Bernstein therefore concludes that, inasmuch as contraction 

 begins nearly y^ second after excitation, and the electrical change 

 culminates at -5-^ second, the mechanical thud must, as well as the 

 electrical, be molecular, and concludes that the two sounds are coin- 

 cident. In the second of these conclusions, Professor Bernstein 

 appears to be justified, but not in the first. It having been shown by 

 the photographic records that the two responses, the electrical and 

 the mechanical, are nearly coincident, it is no longer needful to seek 

 an explanation of the fact that the electrical and mechanical sounds 

 are indistinguishable. 



III. " The Development of the Sympathetic Nervous System in 

 Mammals." By A. M. PATERSON, M.D. Communicated by 

 A. MILNES MARSHALL, F.R.S. Received April 18, 1890. 



(Abstract.) 



The following investigations were undertaken with the object of 

 determining the origin of the Mammalian sympathetic system, and of 

 clearing up thereby certain points in its morphology. 



Two opposite views exist at present among embryologists regarding 

 its development. In both views the segmental formation of the sym- 

 pathetic cord is upheld. According to the older view (Remak, &c.), 

 it is mesodermal, and is formed in situ. According to more recent 

 views, it is ectodermal. Balfour and Onodi, who have maintained the 

 latter view, differ, however, as to the fundamental origin of the 

 sympathetic system, Balfour regarding each sympathetic ganglion 

 as an offshoot from the spinal nerve, while Onodi considers it a direct 

 proliferation from the spinal ganglion. 



For the present research mammalian embryos were exclusively em- 

 ployed rat, mouse, rabbit, and human embryos. The stage in 

 development was first considered in which the sympathetic system 

 was plainly visible, and from this point the earlier and later stages in 

 the process were traced. It was only possible to determine approxi- 

 mately the ages of the embryos employed, as the time of impregnation 

 varies in different instances, and two embryos from the same uterus 

 often differ in size and extent of development. 



The first event to occur is the formation of the main sympathetic 

 cord. In very young embryos (e.g., rabbit, 7 days, axial length 

 5 mm.), in which the spinal nerves are completely formed and the 

 spinal ganglia clear and distinct, there is no trace of the sympathetic 



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