152 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
Following closely upon this observation of Durham, Bedford-Brown 1 demon- 
strated in the same year by observations on a patient having the brain surface exposed, 
as the result of accident, that the induction of anaesthesia caused a primary hyperaemia 
which soon passed off and was succeeded by anaemia. 
Contradictory observations followed on this by various observers, some of whom 
found hyperaemia and some anaemia during anaesthesia, but a critical research by 
Claude Bernard 2 demonstrated the accuracy of Bedford-Brown's observations, and 
there is now little doubt that the observations of hyperaemia were due to the presence 
of inflammation, the result of unskilful trephining, and not to the action of the 
anaesthetic. But while it may be taken as established, from these observations, that 
both sleep and anaesthesia are accompanied by anaemia of the brain, it is obvious for 
various reasons that this can only be a secondary factor or accompaniment, and not 
the primary cause of either condition. 
In the first place, anaesthesia can be produced in organisms in which there is no 
blood supply and even no nerve cells, for anaesthesia is a condition which can be 
impressed upon any living cell no matter how lowly its organization. Hence the 
primary action must be directly upon some constituent of the cell and not solely upon 
something outside, although in the case of the higher cells, such as the cortical cell of 
the mammal, interference with its nutrition by alteration in blood supply may act as 
such a cause and produce anaesthesia. There is no doubt whatever that suddenly 
produced anaemia of the brain, such as occurs, for example, by double compression 
of the carotids, by vagus action upon the heart, or by the sudden hydrostatic fall 
in cerebral blood pressure caused in debilitated individuals by assuming the standing 
position, gives rise at once to an anaesthetic effect and to sudden loss of consciousness. 
But here again the cause of the anaesthesia is something of a chemical nature suddenly 
occurring in the nerve cells, the result of the stoppage or alteration in the cerebral 
circulation, and not a merely mechanical effect produced by the fall of pressure. 
Secondly, although the lessened blood flow in the brain may assist in maintaining 
sleep or anaesthesia, by lessening the metabolic changes in the nerve cells, it is 
quantitatively too slight, acting alone, to produce the whole effect in this manner. 
Thirdly, even admitting that a part of the effect in both sleep and anaesthesia 
may be due to altered blood supply, there remains to be sought out the cause of the 
altered blood supply. This, whether it be a direct effect upon the musculature of the 
blood vessels or be due to an indirect effect through the vasomotor system, must in 
the end arise from some chemical effect of the anaesthetic upon muscle cell or nerve 
cell. 
Hence, while there is probably similarity in mode of causation of sleep (including 
coma) and anaesthesia, such effects as variations in blood supply can only be set 
1 . American Journal of Medical Science, Oct. (i860). 
2. Claude Bernard, Legons sur les Anaesthhiques (1875), p. 117. 
