The subject of this thesis is the outcome of what might be termed a hereditary interest in the complex problem of the relationship of chronic infections to the psychoses and allied mental disorders. Circumstances enabled me, while still a student, to undertake very humbly the continuation of my father's researches in the Scottish Asylums' Laboratory at a point where his illness and death might have proved the closing of a long and arduous chapter. That this would have been so is, as far as I know, borne out by the fact that up to the present no work directly bearing on his later bacteriological studies has been published. The researches I have undertaken during the past six years have been an attempt to elucidate more clearly what exactly are the bacteriological factors at work, and, further, in what manner they attack the economy generally, and with what result. In my endeavour to verify and extend Ford-Robertson's views I have been singularly fortunate.

The diagnosis of syphilis, and especially of latent syphilis, has become a matter of increasing importance in mental hospital practice. The great difficulty hitherto experienced has been in connection with the adoption of some routine laboratory test. As long as the Wassermann was the only serological test available, many institutions were confronted with the task of undertaking a test that was too complex and difficult for all but the best equipped laboratories. This is now so well recognized that it has been very definitely recommended that no hospital should carry out the Wassermann reaction unless it has a well-trained laboratory staff headed by an experienced pathologist, and that even then results should not be relied upon unless the number of tests done each week is sufficient to ensure a continuity of technical practice (82, 83, 107). Furthermore, it has been felt that the Wassermann, good though it may be, is yet liable to error, especially in treated cases (45, 72). A search has therefore been instituted for tests that would be simpler, quicker, and, if possible, more sensitive than the Wassermann. As a result a number of flocculation tests have been devised, and these have been extensively tried by syphilologists and others (1, 5, 20, 23, 62, 88, 97, 99, 102, 114, 134). More recently, these flocculation tests have slowly found their way into mental hospitals, and whereas in the Board of Control Report for 1925 no mention is made of any of these tests, in 1930 no less than six of them were reported upon, one of them apparently having been used in five different hospitals (15, 16, 20, 21, 25, 30, 31, 34-36, 40, 42, 43, 48, 49, 100, 112, 113, 132, 133).

Studies on the leucocytes in various forms of mental disorder have appeared at various times in the literature, and will continue to do so, as long as newer methods of staining, etc., are introduced.

The theory of hæmoclasia, which was first propounded by Widal, rests on the assumption that, during the digestion of proteins, a leucocytosis normally occurs in the blood. When the liver is diseased, proteose substances find their way into the systemic circulation, and produce a series of manifestations characterized by lowering of the blood-pressure, hypercoagulability, leucopenia, decreased refractive index of the blood and fewer blood-platelets. From this discovery a clinical test was evolved, which was at one time believed to be of considerable assistance in estimating the functional efficiency of the liver. In the performance of this test the number of white blood-corpuscles in the circulation is alone taken as a criterion of the presence or absence of hæmoclasia, the other phenomena, e.g., raised blood-pressure, hypercoagulability, etc., not being usually investigated. A white blood-count is performed on a fasting patient, who is then given 200 grm. of milk. Further leucocytic estimations are thereafter made at intervals of twenty and forty minutes, and if a leucocytosis fails to appear, or a leucopenia occurs, the patient is said to exhibit an hæmoclastic crisis.

The object of this paper is to show that certain errors are inevitable when white blood-cells are enumerated, and to demonstrate that results from such enumerations must be interpreted with mathematical considerations. In the past the mathematical applications have, to a large extent, been ignored, and only the actual experimental figures considered. Here an endeavour is made to correlate the two, and to refer to various fallacies that may be present when conclusions from such results are under consideration.