230 IV AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



The physiological observations of Gotch and Horsier 1 indicate that when 

 in a monkey a dorsal root is stimulated electrically 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. This leaves only 5 per cent, of the impulses to pass up by 

 the contra-lateral columns. These experiments, therefore, give less impor- 

 tance to the lateral columns than was to be expected from the observations 

 of Woroschiloff. 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. 



Osawa 8 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 

 permanent disturbance of sensation or motion. 



If the cord was 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 persisted behind the section, although they were somewhat 

 damaged. After three hemisections, alternating 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 some afferent impulses is certainly a tortuous one, and 

 at present not readily to be explained. Tt must be remembered, however, 

 that our information concerning the short pathways in the cord is very slight. 



Nerves of Common Sensation. — In order to analyze the afferent path- 

 ways still further, we next inquire whether among the dorsal nerve-roots 

 which p.-iss between the cord and periphery there are separate nerve-fibres 

 for each of the modes of sensation represented by pressure, heat, cold, pain, 

 and the muscle-sensations. The data available for determination of this 

 question are not of the best, but are still of some value. 



The number of dorsal root nerve-fibres on both sides was estimated (in a 

 woman twenty-six years of age) by Stilling to be approximately 500,000. 4 

 Stilling's estimate for the ventral root fibres in the same individual was 

 300,000. 



The area of the .-kin in a man of (>2 kilograms 1 136 pound-), and twenty- 

 six years of age, was found by Meeh to lie 1,900,000 square millimeters. 8 



From tin' study of the nerves going to the muscles of the dog, Sherring- 



1 Croon ian Lectures: Philosophical Transaction* <</' the Iloyd Society, 1891. 



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



; f'nii ,'.:iii-hiiii(j< n Hbt'r (lie, Leilungsbahnen im Riickenmark des JIundes, Strassburg, 1882. 



1 It seems probable that both these estimates were too low. 



■ \ Blight correction is called for hero, owing to the fact that the area of skin includes that 

 for the head, while the sensory nerves enumerated do not include the fibres going to the head. 

 The genera] relations given below would not, however, be significantly modified by the altera- 

 tion of the data. 



