SPINAL REFLEXES. 835 



between the chelae, is either rejected forthwith, or is made use of for leverage 

 in the attempt to return to position. The " spinal " crayfish similarly placed also 

 " struggles," and will recover normal posture ; but the placing of food 

 in its chelse renders idle the struggling movement of recovery, for there is 

 thus evoked a "feeding" reflex which drafts off some or all of the limbs to 

 carry the morsel to the mouth and tuck it between the jaws, leaving the 

 remaining tilting movements of the limbs quite ineffective. 



In the living severed halves of Hirudo, the reaction of the halves as 

 regards the terminal sucker of each is different. Pressing the sucker of the 

 front half against an appropriate surface usually does not cause it to attach 

 itself, but simply causes the head to be raised and moved vigorously with 

 movements suggesting defence. Pressing the sucker of the " spinal " hind 

 half causes the sucker to be reflexly attached to any appropriate surface 

 (Loeb), 1 in accordance with the spinal reflex nature of sucker reactions in 

 general (Grainger).' 2 A touch on the abdomen or thorax of the decapitated bee 

 causes it to sting itself at the spot touched, 3 the creature dying from its own 

 sting. The decapitated snake winds round a hot bar, 4 just as it winds round 

 a rabbit. 5 The blind fatality of these reflexes justifies the expression that the 

 animal reduced to the " spinal " condition is no longer an individual, but is a 

 mere series of living segments. 



Influence of condition of the central organ. — (1) Vascular condi- 

 tion. — A spinal frog in which the circulation has been arrested by 

 ligation of the base of the heart, or in which the blood has been replaced 

 by normal saline solution, will, by limb movements, continue to respond 

 to skin stimuli for some thirty minutes if its temperature be low ; for a 

 shorter time only if at summer temperature. In the spinal rabbit the 

 reflexes are abolished by arrest of the circulation in less than one minute. 6 

 The reflex reactions of the mammal persist, however, much longer after 

 arrest of the blood supply of the cord if the animal has previously been 

 cooled. 7 The vascular reflexes appear to persist longer than do those 

 employing the skeletal musculature. After an interruption of the 

 circulation in the rabbit by compression of the root of the aorta for 

 forty seconds, the re-establishment of the circulation fails to restore the 

 reflex function of the cord. After low thoracic ligation of the aorta 

 when the hind-limbs are paralysed, stimulation of their skin can still 

 evoke reflex movements from the fore-limbs. This may be due to the 

 long upward nerve fibre path in Goll's column, which is not dependent 

 on synapses in the spinal region. 



When the abdominal aorta of the rabbit is clamped just behind the renal 



arteries for from thirty to sixty minutes, there ensues permanent sensory and 



motor paralysis of the hind-limbs, bladder, and rectum, which has its cause in 



• the necrosis of the grey matter of the lumbar cord. 8 When the animal is 



killed, five to six hours after the sixty minutes' compression, many of the 



1 Arch./, d. gcs. Physiol., Bonn, 1894, Bd. lvi. 



2 "Functions of the Spinal Cord," London, 1837 ; also see Carpenter's Essay, London, 

 1839. 



3 A. Lethe, Arch. f. d. gcs. Physiol., Bonn, 1897, Bd. Ixviii. 



4 Osawa and Tiegel, ibid., 1877, Bd. xvi. S. 90. 



5 Sigmund Exner, " Entwiirf ein. physiol. Erkliir. psychisch. Erscheinungen," Wien, 

 1894. 



6 Charles Bichet, " Thysiol. des muscles et des nerfs," Paris, 1882, p. 716. 



7 CI. Bernard, " Lecons sur le systeme nerveux," Paris, 1857. 



8 Ehrlich and Brieger, Ztschr.f. klin. Med., Berlin, 1884, Bd. vii. ; Singer, Silzungsb. 

 d. k. Akad. d. Wissensch., Wien, 1887, Bd. xcvi. ; Herter, Journ. Nerv. and Merit. Dis., 

 N. Y., 1889 ; Spronk, Arch, dc physiol. norm, ct path., Paris, 1888, Sor. 4, tome i. p. I ; 

 Singer and Miinzer, Denkschr. d. k. Akad. d. Wissensch., Wien, 1890, Bd. lvii. ; Miinzer 

 and Wiener, Arch. f. cxper. Path. u. Pharmakol., Leipzig, 1895, Bd. xxxv. S. 114. 



