On the Reflex Fund ion of the Spinal Marrow. 187 



rific ra^'s, and thattlic introduction of a concave lens tends to 

 achromatize and improve the light. Our solar and oxy-hy- 

 drogen microscopes, therefore, instead of being used for pur- 

 poses of amusement only, and limited to the exhibition of ob- 

 jects which are not affected easily by heat, may henceforward 

 be employed for purposes of scientific ijivestigation, and there- 

 by assume the more important rank of valuable philosophical 

 instruments. 



Peckham, Feb. 10,1837. 



XLII. On Professor Muller's Account of the Reflex Func- 

 tion of the Spinal Marrow. Communicated by Marshall 

 Hall, M.D., F.R.S., 8fc. ( 



[Continued from p. 129, and concluded.] 



"T^R. MARSHALL HALL distinguishes four kinds of 

 ^-^ muscular contraction: 1st, The voluntary, which appears 

 todepend on the brain; 2nd, The respiratory*, which appears to 

 depend on the medulla oblongata; 3rd, The involuntary, which 

 depends on the nerves and muscles, and requires the immediate 

 application of stimuli to the muscles provided with nerves, or 

 lo their nerves ; and 4th, The reflecting, which continues, in 

 part, after the voluntary and respiratory have ceased, and is 

 connected with the medulla spinalis. It ceases after removal of 

 the spinal marrow, though irritability does not diminish. In 

 this fourth the motor stimulus does not originate in a central part 

 of the nervous system, but at some distance from the centre ; 

 it is neither voluntary nor direct in its course, but rather ex- 

 cited by peculiar stimuli, which act, not immediately on the 

 muscular fibres and motor nerves, but on membranous ex- 

 pansions, from which the stimulus is conducted to the medulla 

 spinalis. Dr. Marshall Hall illustrates the importance of this 

 reflecting function of the medulla oblongata and spinal marrow 

 by some instances. The prehension of food is a voluntary act, 

 and cannot be performed after removal of the brain ; the pas- 

 sage of the morsels of food over the glottis and through the 

 pharynx depends on the reflex function, and still continues 

 after the brain is removed. Although, for instance, the 

 muscles whicli are active in this case, may also act voluntarily, 

 yet the presence of the morsel in the pharynx produces a se- 

 ries of violent motions, which have been described above 

 (p. 479.), and which arise from the stimulus of the morsel 



• I am now of opinion that respiration itself is a part of the reflex or ex- 

 cito-motory function, and dependent upon appropriate excitor nerves. — 

 M. H. 



2B2 



