In a series of publications issued from the Institut Prophylactique in Paris, Vernes and his co-workers (1926) described a flocculation method for the diagnosis of tuberculosis in man. This method was first elaborated for the diagnosis of syphilis. Various modifications were then introduced and it was found that the test could be applied to the diagnosis of human tuberculosis. Finally a standard technique was laid down. This consisted of measuring by means of the Vernes-Bricq-Yvon photometer the amount of flocculation which took place during 4 hours' incubation at 20° C. when 0·6 c.c. of resorcinol (1·25 per cent.) was added to an equal volume of the blood serum under test. Readings were taken immediately the resorcinol was added and again at the end of the incubation period. The difference between these readings gave the value on which the diagnosis was made. If this were below 30 the serum was considered normal. Values over 30 indicated infection, the higher the number the more advanced the infection. Correlation of these figures with clinical examination showed that very frequently the photometer value confirmed the clinical findings, and that in some cases the course of the disease could be forecast and followed by testing a number of blood samples over a period.