Some symptoms, e.g., polydipsia and polyuria amounting to a diabetes insipidus, associated with headache and arrested attention, suggested possibly a new growth in the pituitary region. The mental symptoms might naturally be supposed to be due to some infiltration or pressure effect of intracranial growth. After admission to the Psychopathic Hospital, the patient was found difficult to arouse, although he could eventually be aroused. His orientation proved to be as poor as his memory. From time to time, the patient became a bit more intelligent and able to execute requests. The =physical examination= was in general almost entirely negative. =Neurologically=, the pupils were markedly contracted and reacted slowly to light, though they were otherwise normal. The deep reflexes were all somewhat lively, though equal. The umbilical and cremasteric reflexes in particular were present. Systematic examination revealed no other reflex disorder, nor any disturbance of sensation. There was a coarse tremor of the extended hands. There were no phenomena of importance in the visual fields. As against the diagnosis of growth, pituitary or extrapituitary (diabetes insipidus and headache), a hypothesis of neurosyphilis had to be considered. Not only were the contracted, slowly-reacting pupils and the active deep reflexes suggestive, but the euphoria with grandiose ideas looked entirely consistent. As for the polyuria, one had to think of the so-called syphilitic polyuria of the textbooks, which is regarded as a more or less characteristic result of syphilitic involvement of the _basis cerebri_. Moreover, the W. R. in the spinal fluid proved to be slightly positive; 146 cells per cmm. were found therein; there was a large quantity of globulin, and a very marked increase in albumin. These observations seemed to be exceedingly suggestive of a cerebral syphilis. However, as the case progressed, the diagnostic situation changed. The W. R. upon a second puncture fluid proved negative. After some weeks, characteristic symptoms of intracranial pressure developed; the diagnosis of BRAIN TUMOR had to be taken as established, and there is no doubt of its correctness. 1. What is the explanation of the weakly positive W. R. in Safsky’s spinal fluid? An explanation is not easy to find. Possibly we may regard the reaction as an example of error in technique. It is even possible that it may have been produced by exudative products in the spinal fluid. 2. What precautions may be taken against an error in diagnosis such as was first made through the positive spinal fluid Wassermann in the case of Safsky? First, repetition of the W. R.; secondly, it is very unusual to find a weakly positive W. R. in a case with such marked excess of albumin and such very marked increase of globulin as was shown by this case.