NERVOUS MECHANISM OF RESPIRATION. 



2 *5 



of the respiratory nerves are unable, of their own initiative, to carry- 

 out rhythmic respiratory movements, but are subsidiary to the action 

 of a co-ordinating centre situated somewhere above the lower end of the 

 medulla oblongata. 



If, on the other hand, a section be made through the upper part 

 of the medulla oblongata, separating this and the spinal cord from 

 the higher parts of the brain, respiration is absolutely unaffected. It is 

 evident, therefore, that the respiratory centre, or the part of the central 

 nervous system which originates and co-ordinates the respiratory move- 

 ments, is situated in the medulla oblongata, somewhere between its lower 

 part and the stria? acustica?. A number of attempts have been made 

 to localise the situation of the respiratory centre more exactly. From 

 the time of Flourens 

 it has been recognised 

 to be bilateral, as is 

 proved by the fact that 

 bisection of the medulla 

 oblongata by an antero- 

 posterior incision in the 

 middle line does not 

 alter in any way the 

 rhythm of respiration. 

 According to Flourens 1 

 the respiratory centre 

 is represented by a 

 circumscribed spot just 

 below the apex of the 

 calamus scriptorius, of 

 the size of a pin's head. 

 This spot was desig- 

 nated by its discoverer 

 the nceud vital, and 

 according to him, its 

 destruction causes total 

 cessation on the side on 

 which it was destroyed, 

 or, if the lesion be 

 bilateral, an instant 

 and permanent cessa- 

 tion of the respiratory 

 movements on both sides, and consequently the death of the animal. 



In 1873, careful experiments were carried out by Gierke 2 in Heiden- 

 hain's laboratory, in order, if possible, to determine the cells or groups of 

 cells contained in Flourens' centre. Gierke was unable to localise the 

 respiratory centre in any special group of cells, and found that the grey 

 matter lying in the situation of Flourens' centre might be destroyed to a 

 considerable extent, without causing a cessation of the respiratory move- 

 ments. The only part of the medulla oblongata which, according to 

 him, seemed to be essential for the carrying out of these movements, 

 was a longitudinal bundle of white fibres on each side of the median 

 line. This bundle, which was termed the "respiratory bundle" by 

 Krause, and is generally known as the funiculus solitarius, is situated 

 1 Loc. cit. '■> Arch./, d. <jes. Physiol, Bonn, 1873, Bd. vii. S. 585. 



Fig. 169. — Diagrammatic section of medulla oblongata below 

 middle of olivary body, to show region of respiratory 

 centre. ?uc, nucleus of tenth nerve ; X, root of tenth 

 nerve ; nxii, nucleus of twelfth nerve ; fs, funiculus 

 solitarius ; fa, arcuate fibres ; nam, nucleus ambiguus ; cr, 

 restiform body ; p>j, pyramidal tract ; V, ascending root of 

 fifth nerve ; n/ji, nucleus lateralis ; nfc, nucleus of funi- 

 culus cuneatus ; nfg, nucleus of funiculus gracilis. — After 

 Bechterew. 



