SPINAL SHOCK. 845 



from day to day. The very spot of skin that one day evokes nothing but 

 flexion of all the toes, may the next evoke nothing but flexion of the 

 hallux and extension of the other toes ; and the next nothing, or again, 

 only the movement obtained three days before. A stimulus usually 

 eliciting dorso-flexion at ankle may on some days elicit in the same 

 individual plantar flexion of the ankle. As a broad rule, spinal 

 reflexes are more easily elicited when a well-nourished animal is 

 hungry and expecting food, and less easily when it has just heavily 

 fed. There is, so to say, a spinal hunger. The knee-jerk in the dog 

 varies in the same way as the true reflexes in relation to time of 

 feeding. But altogether apart from feeding time, on some days hardly 

 a reflex can be elicited from the very animals that on other days yield 

 a variety of reflexes with readiness. Conditions of individual age, and 

 especially of body temperature and general nutrition, influence, as 

 Freusberg points out for the lumbo-sacral reflexes of the clog, the facility 

 of reflexes very greatly indeed. 



Autotomy. — Among reflex reactions exciting contraction of muscles, an 

 interesting group discovered by Fredericq, execute what he has called autotomy} 

 In many animals, e.g. Asterias, Cometula, Ophiurus, Arachne, insects, and 

 crustaceans, if a limb be pulled upon sufficiently forcibly or long, it is suddenly 

 ruptured across and shed. In the same way some vertebrates (e.g. Anguis 

 fragilis) shed the tail. The reaction is a reflex one, employing muscular con- 

 traction. It can be elicited not only by a bloAV or a crush, but by an induction 

 shock or a chemical irritant. It requires in Asterias the mediation of the 

 ganglion at the base of the ray; the circumbuccal nerve-commissures connecting 

 ray with ray may all be severed without impairing the autotomy, although the 

 reaction is then less easy to obtain. Fredericq's experiments show that the 

 actual mechanism consists, at least in many cases, of a violent contraction of a 

 muscle, so powerful as to break a proximal joint and rupture the tissue. In 

 the crab the muscle employed is the great extensor of the forceps. This 

 contraction does not seem at the disposal of the " will " of the animal. If 

 the limb be gently though effectively fixed, the animal in all its endeavours to 

 escape never performs autotomy. A sudden strong stimulus to the limb itself 

 can provoke reflexly a more powerful contraction of the limb muscle than can 

 be evoked by impulses emitted from the higher centres. 



Spinal Shock. 



" Shock," like " collapse," a term more used by the clinician than 

 the physiologist, is, like it, a term somewhat ill-defined in scope. In 

 some forms of the clinical condition, circulatory disturbance and 

 inspissation of the blood play part, but, as understood by the phy- 

 siologist, " shock " is primarily a nervous condition. " If in a frog the 

 spinal marrow be divided just behind the occiput, there are for a very 

 short time no diastaltic actions in the extremities. The diastaltic 

 actions speedily return. This phenomenon is ' shock.' " 2 Whytt had, a 

 century previous to Hall, drawn attention to the same phenomenon, 

 although assigning to it no descriptive term. The whole of that depres- 

 sion or suppression of nervous function which ensues forthwith upon a 



1 L^on Fredericq, Arch, de zool. exper., 1883 ; Arch, dc biol., Gand, 1882, tome iii. p. 235 ; 

 Rev. scient., Paris, 1886, p. 613; 1887, p. 1 ; Trav. du lab. de Marcy, 1887-88, tome ii. 

 p. 201 ; ibid., 1894, tome iv. ; Preyer, Mitth. a. d. zool. Stat, zu Nca2xl, 1887, Bd. vii. 

 S. 203 ; Jean Demoor, Trav. d. 1. slat. zool. d. Hcldcr, 1891, p. 130. For other refer- 

 ences see papers by Fredericq. 



- Marshall Hall, "Synopsis of the Diastaltic Nervous System," London, 1850. 



