CH. XLVIII.] SLEEP AND NARCOSIS 699 



nerve units are in contact with each other ; transmission of nerve 

 impulses from neuron to neuron is then possible, and the result is 

 consciousness; during sleep the dendrites are retracted in an 

 amoeboid manner ; the neurons are therefore separated, and the result 

 is unconsciousness. 



Lugaro, on the other hand, takes the precisely contrary view. 

 He was not able to discover moniliform enlargements, and his bio- 

 physical hypothesis is that the interlacing of dendrites is much more 

 intimate during sleep than during consciousness. He therefore 

 explains sleep by supposing that the definite and limited relation- 

 ships between neurons no longer exists, but are lost and rendered 

 ineffective by the universality of the connecting paths. It is not 

 very difficult to explain such divergence of views, for they both 

 depend mainly on observations made by a single method ; and the 

 method itself is open to objection. It is one which gives even in the 

 same brain most inconstant results, and is not calculated to show 

 much more than a mere outline of a few of the cells and their 

 branches. So much doubt has arisen of late in regard to the trust- 

 worthiness of the method, that many neurologists are beginning to 

 doubt whether the neuron theory implying absolute non-continuity 

 of nerve units has been satisfactorily proved, and there is a tendency 

 to return to the idea of a connecting network not very different from 

 that originally put forward by Gerlach. 



A more satisfactory investigation of the effect of anaesthetics on 

 nerve-cells was carried out by Hamilton Wright. 



He used rabbits and dogs, and subjected them to ether and 

 chloroform narcosis for periods varying from half an hour to nine 

 hours. In both animals he found that the nerve-cells are affected, 

 but in rabbits much more readily. This accords quite well with 

 what is known regarding the susceptibility of rabbits as compared to 

 dogs towards the influence of these narcotising agents. In a rabbit, 

 the nerve-cells, especially of the cerebrum, show changes even after 

 only half an hour's anaesthesia, but in dogs at least four hours' anaes- 

 thesia must be employed. By the Golgi method the moniliform 

 enlargements can be seen. These become more numerous, larger, 

 and encroach more and more on the dendritic stems, the longer the 

 anaesthesia is kept up. The accompanying illustrations show the 

 appearances seen (fig. 508). 



Lugaro's failure to find these appearances is doubtless due to his 

 not having maintained the anaesthesia long enough in his dogs. 



Wright started his work with a bias in favour of Demoor's bio- 

 physical theory, but he soon found that the theory was untenable ; 

 the results of his observations have shown him that the action of 

 anaesthetics is bio-chemical rather than bio-physical, and he has been 

 led to this conclusion by the employment of other histologica] 



