LOSS OF NERVE CELLS IN EXPERIMENTAL CEREBRAL CONCUSSION

It is largely on the basis of experimental work performed during the past decade that concussion of the brain can with confidence be described as a discrete, traumatic cerebral affliction. It is induced instantaneously when the head strikes an object, or is struck, under conditions in which the cofactors of transfer of adequate mechanical energy to the brain, in a sufficiently brief interval, are operative. Concussion can occur as an uncomplicated phenomenon, and as such may be either reversible or, in animals and presumably in man, irreversible terminating in death. It can, in addition, prevail as a complication in the more overt forms of brain injury, and here, likewise, it may be reversible, or it may be the sole or a contributing cause of death. Henceforth in this paper, we shall deal only with uncomplicated, reversible concussion. A good deal of awkwardness of expression is encountered in discussing concussion. This stems from the usage of the term 'concussion' to characterize both the mechanical incident which produces injury and the state of the injured individual for some indefinite interval afterwards. Further complication is introduced by use of the term 'post-concussion,' which can be no more precise in meaning than the word from which it is compounded. As a remedy, it is suggested that the term 'concussion' be applied only to the state of an individual in whom appropriate functional and structural alterations exist following a mechanical shock to the brain, but that the term 'concussion' never be used to refer to the mechanical events which initiated the changes. Concussion may be divided into three phases: basic, early, and late. The basic phase is a fleeting episode in which the brain is overwhelmed by the concussing shock and much of its nervous structure acutely altered in organization and activity. The most recent theory of the genesis of these alterations is the wellconceived notion that the formation and collapse of scattered, minute cavities in the fluid component of the brain tissue, respectively during and after the brief negative phase of the percussion wave passing through it, produce transient local shearing forces which affect the tissues (16). All the histological and functional changes which ensue are direct consequences of the injuries inflicted upon the nervous tissue in the basic phase. In the early phase, disturbed organization and function tend to be gradually restored, but some neural elements, damaged beyond repair, progressively degenerate. The late phase is a residual state, char-