CENTRAL NERVOUS SYSTEM. 671 



this animal the reaction was most diminished that is, stimulation of the 

 sciatic produced least rise in the blood -pressure when the lateral columns of 

 the cord had been cut through ; and that the effect of section of the lateral 

 column on the side opposite to that on which the stimulus was applied was 

 greater than that following section of the column on the same side. These 

 experiments are open to the criticism that the results are proved only for a 

 very limited set of conditions, and hence it would be unwise to make any 

 broad inference from them ; yet at the same time they form a very definite 

 part of the evidence which directs our attention to the lateral columns of 

 the cord as a principal afferent pathway. 



The physiological observations of Gotch and Horsley l indicate that when 

 in a monkey a dorsal root is stimulated electrically, then 80 per cent, of the 

 impulses pass cephalad on the same side of the cord, while the remainder cross. 

 Of the 20 per cent, that cross, some 15 per cent, pass up in the dorsal columns. 

 The dorso-ventral median longitudinal section of the cord in the monkey 

 (sixth lumbar segment) 2 shows an ascending degeneration in a small part of 

 the dorsal area of the direct cerebellar tracts and of the ventro-lateral tracts, 

 as well as in the columns of Goll. This would indicate that the section had 

 cut fibres which crossed the middle line and ran cephalad in these localities. 



These investigations all point to the several tracts most closely connected 

 with the dorsal nerve-roots as the paths for the sensory impulses. The experi- 

 mental results, taken together, are by no means accordant, but not necessarily 

 mutually exclusive : confusion must, therefore, not be permitted to enter here 

 through any unwarranted attempt to combine observations which should really 

 be kept apart, and the failure of which to harmonize is in large degree an ex- 

 pression of the physiological complexity of the cord. 



Osawa 3 found that when the cord in a dog was hemisected (in the upper 

 lumbar or lower thoracic region) the animal showed for the most part no per- 

 manent disturbance of sensation or motion. 



If the cord is first hemisected on one side, and later on the other side, the 

 second hemisection being made a short distance above or below the first, sen- 

 sation and motion persist behind the section, although they are somewhat 

 damaged. After three hemisections, alternating and at different levels, there 

 still remained a trace of co-ordinated movement possible to the hind legs, 

 although the sensibility of the parts could not be clearly demonstrated. The 

 path thus marked out for any afferent impulses is certainly a tortuous one. 

 These observations were followed by a number of others, the most important 

 of which in this connection are the following : 



Section of all parts of the cord except the two lateral columns (in the lower 

 thoracic region, Fig. 176) was without influence on the sensibility or move- 

 ments of the hind legs. After section of the entire cord, with the exception of 

 the dorsal and ventral columns and the intervening gray matter, sensation was 



1 Croonian Lectures, Philosophical Transactions Royal Society, 1891. 



2 Griinbaum : Journal of Physiology, 1894, vol. xvi. 



s Untersuchungen uber die Leitungsbahnen im Riickenmark des Hundes, Strassburg, 1882. 



