ON THE MAMMALIAN NERVOUS SYSTEM. 



433 



which was accompanied by reflex movements, was 210 with the columns intact, and 

 after their division at the level of the 12th dorsal vertebra, sank to 3G. 



In the Monkey this marked diminution was also found. Thus in a Rhesus the cord 

 was divided at the lower border of the 6th dorsal vertebra, and prepared as before. 

 Excitation of the right sciatic nerve evoked a cord effect of 82 ; excitation of 

 the left sciatic an effect of GO ; after division of both posterior columns at the level 

 of the lower border of the llth dorsal vertebra, excitation of the right sciatic 

 produced an effect of only 18, and that of the left sciatic an effect so small as to 

 be indicated by a mere trace, viz., 2. 



It need scarcely be pointed out that the presence or absence of concomitant reflex 

 movements as an index of the awakened corpuscular activity of the cord is a most 

 important factor to be borne in mind, but the diminution occurs even when a more 

 pronounced stimulus of greater duration is used, as is shown by the following 

 experiment on a Rhesus Monkey. The cord was divided at the 8th dorsal vertebra, 

 and prepared for galvanometric observation. The right sciatic was excited and 

 evoked a reflex movement and large effects, indicated in repeated observations by 

 deflections of 210, 300, and 308. The left sciatic gave effects of 230, 250. After 

 section of both posterior columns, the effect sank to 55 and 58 following excitation of 

 the right nerve, and to 90 and 60 following excitation of the left nerve. 



If now we sum up the various readings (15) obtained in two Cats and two Monkeys, 

 we find, as expressed in the following table, that the intervening section reduces the 

 massed results in the ratio of 100 to 22, that is, both the posterior columns are 

 directly concerned with the production of 78 per cent, of the total effect, and the 

 transmission of the same percentage of impulses. 



TABLE of Readings. Section of Posterior Columns. 



This relationship is confirmed by a control experiment of the reverse kind in which a 



MDCCCXCT. B. 3 K 



