ON THE MAMMALIAN NERVOUS SYSTEM. 281 



instant effect of ether inhalation is a remarkable fall in blood-pressure, such a fall 

 in blood-pressure as the early experiments of VULPIAN showed would of itself, if 

 sufficiently pronounced, cause a diminution in the functional activity of all the 

 nerve elements, such diminution occurring first and most markedly in the centres, 

 and even a comparatively slight fall may be followed by a loss in the excitability of 

 these, although the nerve fibres might not be appreciably affected. 



The effect of ether, therefore, in diminishing the excitability of the cortex and 

 lowering its functional activity may be in part due to changes in the circulation. 

 It is probable, however, that the ether in the blood exercises a direct toxic effect 

 upon the nerve structures, of a similar kind to that which is brought about by the 

 direct action of the vapour already alluded to. We are not aware of any experiments 

 as to the direct toxic action of ether vapour upon nerve centres ; but it is extremely 

 probable that such action occurs and that the centres should be affected by an 

 amount of ether in the circulating blood which is too small to affect in any sensible 

 degree the fibres. 



Whatever the share which the two factors, blood-pressure changes and ether in the 

 blood, may respectively have in the production of the effect, the result is that 

 profound general narcosis serves to abolish the functional activity of nerve centres 

 before that of nerve fibres. We have therefore made use of etherisation, with due 

 caution, to assist us in analysing the compound excitatory effects observed when a 

 complex structural arrangement of centres and fibres has been stimulated, and we 

 have in all cases observed great care in noting as accurately as we could the degree, 

 whether profound or slight, of narcosis at the time of each experimental observation. 



There is one possible disadvantage in the use of large quantities of ether during a 

 considerable period of time which is not very obvious at first sight, and that is the 

 amount of vapour which is present in the air of the room. It did not occur to us that 

 this could act injuriously upon the preparations under investigation until we noticed 

 in three prolonged experiments in which, owing to the method of inhalation, a large 

 quantity of ether was used in a warm close room, that both the exposed cortex and 

 the sciatic nerve suddenly lost their excitability, which they did not regain. The 

 possibility of this being due to that injurious action of the ether vapour dissolving in 

 the liquids upon these structures, which was pointed out by BIEDERMANN, then 

 occurred to us. The effect of the vapour in the room was increased, perhaps, by its 

 dissolving in a warm bath containing 0'6 percent, saline, which mixed with the blood 

 of the animal was employed for irrigation, &c., of the nerve structures. Although 

 the failure might have been due to other causes (exposure, &c.), still the fact of its 

 not occurring when special precautions were taken to avoid the excessive evaporation 

 of ether into the room and the contamination of the saline, leads us to conclude that 

 the cause mentioned is at any rate a depressing factor which ought, as far as possible, 

 to be excluded. 



The use of chloral or morphia would undoubtedly entirely exclude any error of this 



MDCCCXCI. B. 2 o 



