viii CONDUCTIVITY AND EXCITABILITY OF NERVE 75 



partial intoxication. A leech was divided into three parts by two 

 ligatures; the ligatures stopped the circulation without crushing 

 the ventral cord. Strychnin (O'OOOo gm.) was then injected 

 into the middle section, the effect, according to Luchsinger, 

 depending wholly upon temperature. If the leech had been 

 left for some time in water of about 8 C. it showed no sign 

 of excitation, whereas the strychninised section of an animal that 

 had previously been exposed to 25 30 gave lively manifesta- 

 tions of excitation. " Waves of excitation ran from segment to 

 segment, and if these quieted down, the least stimulus to the skin 

 of the animal evoked disorganised movements." The unpoisoned 

 ends throughout remained quiet. After a certain time the centre 

 was paralysed. From this it would appear that there is no radical 

 difference in the reaction of the spinal ganglia to strychnin in 

 vertebrates and invertebrates, though gradations of sensibility 

 are undeniable. The striking effect of temperature upon the 

 action of strychnin, as exhibited in the leech, appears to some 

 extent in the frog also, where it was first observed by Kiihne, 

 and subsequently worked out by Wundt. 



Stronger doses of strychnin produce both in vertebrates, and 

 even more rapidly in invertebrates, a condition similar to par- 

 alysis, the cause of which as of the antecedent rise of excita- 

 bility is central in origin. The behaviour of the animal in this 

 stage of strychninisation is highly suggestive of narcosis from 

 anaesthetics (ether, chloroform, alcohol). We have already studied 

 the peculiar effect produced by these reagents on all contractile 

 substances, as also on nerve-fibres. The ganglion - cells must, 

 however, be ranked first in order of sensibility, in all animals. 



The depressing effect of anaesthesia upon the reflex move- 

 ments of vertebrates has long been known, and it may reasonably 

 be concluded that the ganglion -cells of the centres are first 



o o 



and most profoundly affected in their normal vital properties by 

 the substances in question as shown by the final and complete 

 loss of excitability and conductivity. It was Claude Bernard who 

 first pointed out that the action of anaesthetics is universal, and 

 takes effect upon all excitable protoplasm. All experiments, 

 however, show that the different tissues in an organism are 

 affected in very different degrees. On submitting man, or any 

 vertebrate, to the action of chloroform or ether, it is the sensitive 

 protoplasm of the cells of the cerebral cortex that is pre-eminently 



