LIFE AND MECHANISM. 41 A cell may superficially resemble a mechanism in its be- haviour. But that it is not really a mechanism may be deduced from a consideration of the behaviour of the cells which morphologically correspond to it in the lower animals. The lower we go in the scale of multicellular animals, the more clear does it become that the cells are fundamentally alike in manifesting purposive behaviour. In the higher animals, however, differentiation of function among the cells has gone so far that they have much more the super- ficial appearance of being mechanisms, with the prominent exception of the ganglion-cells of the higher nervous centres. This interpretation of the facts is strengthened by a con- sideration of what may be observed in connexion with pathological conditions of the human body. When any part of a machine is injured or destroyed, there is no tendency to its spontaneous repair. If the injury is repaired, this is only brought about by interference from without. But in the case of injury of any part of the human body there is a manifest tendency to restoration of the function of the injured part, and this quite apart from interferences from without. Sometimes this restoration of function is brought about by means of the reproduction of tissue that has been destroyed, as, for instance, occurs when the shaft of a long bone that has been destroyed by inflammation is reproduced again entire. More frequently, however, this reproduction is due to neighbouring parts modifying them- selves so as to be capable of carrying on the function of the part that is lost. As a good instance of this, may be taken a case of locomotor ataxy recorded by Professor Schultze. 1 In this disease, which is very rarely recovered from and almost always ends fatally sooner or later, there occurs progressive destruction of the fibres of the posterior columns of the spinal cord. The symptoms are very marked, as would be expected from the fact of such an important part of the body being affected. Professor Schultze's patient presented the fully developed symptoms of the disease ; but, contrary to the usual rule, recovered, there being hardly a trace of the disease left. He died some years later from the effects of an accident. When the spinal cord was examined post mortem, the posterior columns in the lower part of the cord were found to be destroyed in the manner characteristic of the disease. The process of wasting had doubtless stopped at the time w r heii the symptoms of the disease began to disappear ; and other parts of the cord had thus been given time to modify themselves in such a way as to reproduce the function of the lost part. 1 Arcliiv fiir Physiologic., xii., s. 232.
