THE DOCTRINE OF HUMAN AUTOMATISM. 267 



ments of which the "purposive" character is more obvious, than 

 it is in the acts of coughing and sucking • the former of which we 

 knowexperientially to be executed without any conscious intention, 

 and to be capable of being excited in states of the profoundest coma 

 that is compatible with the continuance of ordinary breathing; 

 while the latter, although requiring a still more complex combina- 

 tion of the movements of respiration with those of swallowing, can 

 be shown to be a purely " reflex " act, being at once excited by 

 the impression made on the lips of a new-born mammal, even 

 when, in the case of a puppy or guinea-pig, the whole of the brain- 

 proper has been experimentally removed, or when the human 

 infant has come into the world with its spinal cord and medulla 

 oblongata intact, but without any higher nervous centre. 



It was while the doctrine of reflex action without the necessary 

 participation of sensation was thus fighting its way to a place in 

 the general scheme of neuro-physiology, that another very important 

 advance was made by investigations of an entirely different nature, 

 which gave it a cogency and completeness to which it could not 

 otherwise have laid claim ; — I refer to the establishment of the 

 essential distinction, alike in structure and in function, between the 

 two forms of nerve-substance that are known in human anatomy as 

 the " grey " and the " white " matter. The determination of this 

 distinction, which is one of even more fundamental importance 

 than that established by Bell between the motor and sensory nerves, 

 was not the work of any one physiologist. It had long been 

 known that the white portion of the brain, the white strands of the 

 spinal cord, and the entire substance of the nerve-trunks, have 

 a fibrous structure ; and the advance of histological research 

 (which sprang from the application of the principle of achromatism 

 to the uiicroscope) demonstrated that these fibres were ultimately 

 resolvable into tubules of extreme minuteness. On the other hand, 

 the " grey " matter which forms the convoluted layer of the surface 

 of the cerebrum, but which occupies the interior of the spinal cord 

 and the ganglia of the sympathetic system, as it does of the gang- 

 lionic nerve-centres of Invertebrata, was found to be made up of 

 cells or vesicles, certain extensions of which communicate with each 

 other, whilst others become continuous with the fibres of tlic nerve- 

 trunks. The difference in the relative supply of blood which these 



