In the consideration of these localizing symptoms, it must be borne in mind that brain lacerations are of an exceedingly gross nature, and that there may be--as the late Professor von Bergmann[34] pointed out--‘notwithstanding the severest brain symptoms, not the slightest discoverable anatomical alteration in the brain. On the other hand, notwithstanding the absence of all brain symptoms, extensive and striking destruction of the brain substance.’ B. General symptoms. Concussion or cerebral shock. _Its pathology._ Concussion used to be regarded as implying a ‘molecular disturbance’ of the brain--a definition so unsatisfactory that it may be relegated to a desired obscurity. At the present day, though some difference of opinion exists as to whether the condition is or is not necessarily dependent in its development on associated cortical or subcortical lesions, macroscopical or microscopical, concussion is regarded as implying a condition of _acute cerebral anæmia_ through sudden inhibition or paralysis of the vaso-motor centre. With respect to the existence of visible lesions of the brain, Kocher maintains that such lesions--hæmorrhages and the like--are necessarily present, proposing that the term ‘brain concussion’ should be eliminated in favour of ‘brain contusion’. On the other hand, the late Professor von Bergmann pointed out that such a course was not possible, instancing the many cases of concussion where contusion could not possibly have existed. There cannot, in my opinion, be any question as to which is the correct view. It is unreasonable to ask one to believe that the milder cases of concussion, cases in which the patient merely suffers from loss of consciousness for a few minutes, from which he rapidly recovers and is discharged from treatment within a few days, and from which he suffers in the future from no remote ill effects whatsoever, it is unreasonable to ask one to believe that such cases have experienced so severe a lesion as brain contusion or laceration. Both these conditions would require a long period of convalescence, and would tend to leave in their train very serious after-results. It is obvious, therefore, that there exists a degree of concussion from which the patient can quickly and entirely recover. It is also clear that in many cases the patient passes through a long and serious illness, whilst, in some cases, a fatal termination may ensue--and that too within a few hours. It is consequently clear that we have to deal with varying grades of concussion, some of which are of so mild a nature as to be clearly unassociated with definite cerebral lesion, whilst others are of so serious a nature that death may take place within a few hours, and in such cases the gravest cerebral lesions may be found at the autopsy. In other words, it would appear that concussion is more or less dependent in its severity on the degree of associated cerebral change.