1. In the secondary and tertiary stages of syphilis without direct involvement of the nervous system the cerebro-spinal fluid yielded the butyric acid reaction of feeble intensity. The fluid under these conditions gave neither a positive cytodiagnosis nor the Wassermann test for syphilis.
2. The cerebro-spinal fluid of cases of hereditary syphilis showed a positive butyric reaction in about 90 per cent. and a positive Wassermann test in about 80 per cent. of the cases examined.
3. The cerebro-spinal fluid of cases of cerebral and spinal syphilis yielded the butyric acid reaction and the cytodiagnosis in every instance (100 per cent.) and gave the Wassermann reaction in from 50 to 75 per cent. of those examined.
4. The cerebro-spinal fluid from cases of general paralysis gave positive butyric acid reactions in 90 per cent., positive cell counts in 91 per cent., and positive Wassermann test in 73 per cent. of those examined.
5. The cerebro-spinal fluid from cases of tabes dorsalis gave positive butyric acid reactions and cell counts in 100 per cent. and positive Wassermann test in 53 per cent. of those examined.
6. The cerebro-spinal fluid from other forms of psychosis in which a syphilitic history was not obtained gave positive butyric acid reactions and cell count in 2.8 per cent. and Wassermann test in 13 per cent. of those examined.
7. The cerebro-spinal fluid from cases of acute inflammatory diseases of the meninges always gave a flocculent precipitate with the butyric acid reaction but never gave the Wassermann test.
8. The cerebro-spinal fluid from persons suffering from typhoid fever, pneumonia, pulmonary tuberculosis, etc., in which the meninges are not inflamed, gave neither the butyric acid nor the Wassermann test.
9. We think it justifiable to conclude that the butyric acid reaction affords a ready means of distinguishing normal from pathological cerebro-spinal fluid and will prove to be useful in routine clinical practice, especially in detecting syphilitic disease and in confirming or setting aside certain doubtful diagnoses of syphilitic or metasyphilitic lesions of the central nervous system. The reaction should commend itself as a valuable addition to the Wassermann test, the results of which it is capable of confirming and extending.