This rapid fatigue, which only permits the visual acuity present to be estimated for a short period at a time, may easily result in the visual acuity being supposed to be worse than it is. The other phenomenon above mentioned, which occurs in defective vision without being actually a necessary symptom, is the depreciation of the central visual acuity, which we designate as central scotoma in acquired amblyopia. It should be remembered that the visual acuteness which we determine under these conditions is something different from what we are usually accustomed to designate by this idea. When we simply talk of visual acuity we always imply the central visual acuity; however, in cases where the centre of the retina is so injured in its function, that the peripheral parts lying near are too often called into requisition, we do not determine the central visual acuity at all, but that of the nearest and at the same time best, excentric part. We cannot prevent patients from using that part of the retina which seems best to them for recognising the test objects. In such cases (just as in acquired central scotoma) continuous print is read badly, and with more trouble than one would expect from the visual acuteness which is specified in the recognition of single letters. Of course spelling and reading are two different things; the excentric visual acuity may perfectly suffice for the recognition of single letters, central and also excentric visual acuity is necessary for reading. There are patients who, despite full visual acuteness, are unable to read continuously, as soon as a defect in the right half of the visual field extends close to the fixation point. To read fluently, the excentric vision must work on in advance for the width of several letters, but if the first letter is seen excentrically, the excentric visual acuteness rapidly sinking in a physiological way, does not suffice for the following ones.