266 PHYSIOLOGY CHAP. 



period or time of recovery, which lasts 0'25-0'5 sec., during which 

 they are incapable of transmitting impulses to the motor elements 

 of the ventral half of the cord. The latter, on the contrary, are 

 still, under normal conditions, able to react to a series of stimuli 

 thrown in in rapid succession, which evokes tetanic contractions of 

 the corresponding muscles. 



Finally, in another series of researches, Baglioni studied the 

 action of many derivatives of phenol, and saw that while some of 

 these, such as the di- and tri-phenols, have the same exciting action 

 as carbolic acid, others produce an initial depression ; others, again, 

 like benzoic and salicylic acids, have no action on the nerve- 

 centres. 



From these observations as a whole, as well as from the varying 

 capacity of resistance to asphyxia shown by the individual parts of 

 the cerebrospinal axis, it is obvious that there are fundamental 

 differences between the peripheral and central nervous systems, 

 and also between the different elements of the central system 

 functional differences that certainly cannot be reconciled with the 

 theory of equivalence or physiological identity of all the elements 

 that make up the nervous system. 



Unlike the peripheral nerves, the central grey matter has 

 a very active metabolism, and is therefore highly vascular. In 

 this connection Fritsch made an important observation to the 

 effect that the large ganglion cells of the nuclei of origin of 

 the vagus and trigeminus nerves in Lophius piscatorius are 

 traversed by a network of capillaries which is essential to their 

 nutrition. 



The need of a blood-supply for the function of the nerve- 

 centres is shown by the effects of blocking the vessels which supply 

 them. A diminished flow of blood to the brain by rapid compres- 

 sion of the two carotids suffices to abolish consciousness, and in 

 many cases produces a fainting fit, owing to the incapacity of the 

 grey matter to function, due to anaemia. Stenson's experiment 

 (cited elsewhere) that compression or ligation of the abdominal 

 aorta of the rabbit, is quickly followed by paralysis of the hind 

 limbs, shows that anaemia of the spinal cord makes the ganglion 

 cells incapable of function. 



Fredericq repeated Stenson's experiment on dogs in order to 

 determine more accurately the time required to produce motor and 

 sensory paralysis. Fifteen to twenty seconds after the occlusion 

 of the aorta there was a transitory motor excitation of the muscles 

 of the limbs, followed by motor paralysis which became total in 

 30-40 sees. During this time the sensibility of the lower limbs 

 is unaltered ; it is only after 90 sees, that hyperaesthesia followed 

 by anaesthesia sets in, which becomes total about 3 niins. after 

 occluding the aorta. If the compression or the ligature is removed, 

 sensibility returns after 5-10 mins., and motility somewhat later. 



