the test. In such a case the defective sensibility of the abnormal parts to the strongest suitable stimulation is still more evident, and we record that no threshold could be obtained.
The results of all sensory testing depend greatly on personal factors in the observer. We endeavoured to obviate this source of error as far as possible by sharing the various examinations between us. In cases of injury to peripheral nerves or spinal cord the patient was tested by each of us in turn; with lesions of the higher centres we took notes and examined alternately.
2. The Results of our Observations are recorded in Terms of the Tests employed.
In every instance we report the results obtained by sensory examination in terms of the tests we have employed. Such expressions as "joint sense," "muscle sense," "bathyæsthesia," "stereognosis," are strictly avoided; "deep sensibility" has been used as a general heading only to cover several different qualities of sensation arising in subcutaneous tissues, each of which is recorded under some particular test.
Failure to adopt this principle leads to infinite confusion. For, owing to the regrouping of afferent impulses on their way from the periphery to the higher receptive centres, no one of these expressions can have the same significance at different sensory levels. Thus the term "deep sensibility," as commonly used, differs profoundly with lesions in various parts of the nervous system. A peripheral injury which destroys all the cutaneous branches to any part of the body leaves "deep sensibility" intact. The patient not only recognises the posture of segments of the limb and the vibrations of a tuning-fork, but he can appreciate the tactile and painful aspects of pressure; moreover, he can localise with accuracy the position of the stimulated spot.
If the lesion is situated in the posterior columns of the spinal cord "deep sensibility" is also said to be affected; but the qualities which are lost under these conditions do not correspond to the varieties of sensation which remain intact after the destruction of the nerves to the skin. The patient, it is true, has lost the power of recognising posture, passive movement and vibration, but retains complete appreciation of touch and pain, however evoked.
Even such terms as "thermal anæsthesia" should be avoided when reporting clinical observations. For, although lesions of the spinal cord may disturb the appreciation of heat or of cold independently of one another, this is not possible with lesions of the peripheral nervous system. Here response to the grosser thermal stimuli depends on the heat- and cold-spots, punctate end-organs which react in a strictly specific manner. These minute sensitive areas are scattered irregularly over the surface of the body, but cannot be affected independently by any injury to peripheral nerves. Dissociation, when it occurs at this level, consists of a separation of the cruder,
