and subcutaneous tissues, especially when the point is not very sharp, the lumen becomes clogged so that the flow of fluid is partly or completely interfered with. The obstruction is readily removed by passing a wire stylet through the needle. About 7 or 8 c.c. of the fluid is collected in a test tube. If too much fluid is removed the patient is apt to develop severe headaches, attacks of syncope, and vomiting, which may persist for two or three days. In any event the patient should be kept in bed for two days after the operation. The fluid should be examined as soon as possible after it has been obtained, preferably within an hour, as standing produces changes affecting especially the cellular elements. Perhaps of greatest help in diagnosis is the cell count, for which one has to have (1) a Thoma-Zeiss mixing pipette like that used for making white blood corpuscle counts, (2) a Fuchs-Rosenthal counting chamber, ruled as shown in the accompanying illustration, (3) a clinical microscope, and (4) the following staining solution: Methyl violet. Glacial acetic acid. 0.1 gm. 50.0 c.c. 2.0 c.c. This staining solution is drawn into the pipette up to the mark 1 and then the spinal fluid, after being thoroughly shaken to insure uniform suspension of the cells, up to the mark 11; the pipette is then shaken for about five minutes thus mixing the stain thoroughly with the fluid and allowing the acetic acid which is in the staining solution sufficient time to act upon and render invisible any red blood corpuscles with which the fluid may be more or less contaminated and which might otherwise interfere with the count and become a source of error. As the fluid which is in the stem of the pipette does not become mixed with that in the bulb and is drained off before a drop is taken out for the counting chamber, the dilution in the bulb, in calculating the results, is to be considered as in the proportion of 9 parts of spinal fluid to 1 part of staining solution. FIG. 1. RULING OF FUCHS-ROSENTHAL COUNTING CHAMBER. After draining off the fluid in the stem of the pipette, - a drop or two, a drop of suitable size is placed in the counting chamber, the cover glass put on, and the count made after about a minute or so, i.e., after the cells have subsided to the bottom of the counting chamber so as to be as nearly as possible in the same focus as the ruling of the chamber. The count is made most conveniently under rather low magnifying power (16 mm. objective, 10x eyepiece, Bausch and Lomb; or No. 3 objective, No. 4 eyepiece, Leitz). The dimensions of the counting chamber are 4 mm. on each side and 0.2 mm. in depth, i.e., 3.2 cu. mm. As but 0.9 of the mixture in the counting chamber is spinal fluid, the remaining 0.1 being staining solution, all the cells counted in one chamberful represent the cell content of 2.88 cu. mm. of spinal fluid. It is customary to express the findings in number of cells per cu. mm. of spinal fluid; and this is, of course, derived simply by dividing the total number of cells counted over the entire ruled area of a FuchsRosenthal chamber by 2.88. It is always advisable to make two or three counts and report the calculated average rather than the result of a single count. The number of cells per cubic millimeter of spinal fluid varies considerably both in health and disease, and there is no definite point of demarkation between the two. Most pathologists consider any number under 5 as a negative finding, between 5 and 10 as doubtful, and over 10 as positive. Where the clinical data would lead the physician to expect a positive finding while the actual finding is doubtful or even negative, the lumbar puncture may be repeated at the end of ten days. Either on first or second examination almost all cases of general paresis and cerebral syphilis furnish a positive finding; other psychoses furnish, on the contrary, almost invariably a negative one. § 2. WASSERMANN REACTION. The Wassermann reaction has become an important aid, in some cases an indispensable one, in psychiatric diagnosis. It may be applied either to the blood or to the cerebro-spinal fluid, or to both, and may be of assistance (a) in differentiating psychoses of syphilitic nature from others, (b) to some extent in differentiating general paresis from cerebral syphilis and from cerebral arteriosclerosis of syphilitic origin, and (c) in judging the effect of anti-syphilitic treatment.1 Principle of the Wassermann reaction. When blood corpuscles of an animal of a given species are injected into an animal of a foreign species the blood serum of the second animal develops the power of destroying the corpuscles of animals of the first species, that is to say, a specific hæmolytic power. When the serum of an animal thus immunized is heated for an hour at 56° C., or when it has been allowed to stand at room temperature for twenty-four hours, it loses its hæmolytic power, technically it is said to have become inactivated. It may, however, be reactivated, that is to say, its hæmolytic power 1911. --- 1 H. Noguchi. Serum Diagnosis of Syphilis. Philadelphia, Rosanoff and Wiseman. Syphilis and Insanity. A Study of the Blood and Cerebro-spinal Fluid. Am. Journ. of Ins., Jan., 1910. Kaplan. Serology of Nervous and Mental Diseases. Philadelphia, 1914. may be restored, by the addition of serum from another animal, one which has not been immunized and the serum from which, therefore, does not by itself possess hæmolytic power. It is concluded from these facts that the hæmolytic power of the serum of an immunized animal is dependent upon two substances: one which is chemically unstable (being easily destroyed by moderate heat or by standing at room temperature) and nonspecific (being present in fresh serum of non-immunized animals as shown by reactivation), and another which is chemically stable (resisting the effect of moderate heating, etc.) and strictly specific (being present only in the serum of animals which have been immunized by injections of corpuscles). The first substance is called complement, the second amboceptor. For specific hæmolysis to occur, then, the following ingredients are required, constituting a haemolytic system: blood corpuscles + complement + hæmolytic amboceptor. In the case of bacteria the mechanism of immunization is similar; accordingly, the essential ingredients in a reaction of specific bacteriolysis, constituting a bacteriolytic system, are: bacteria + complement + bacteriolytic amboceptor. It was shown by Bordet and Gengou that in any bacteriolytic reaction a definite proportion of complement is used up, and that the amount of complement thus "absorbed" or "fixed" may be used as a measure of the immunity reaction. So that if upon |