Serum from patients with myelomatosis differs from normal serum in various ways. What has chiefly attracted attention is an increase in the serum protein, mainly in the globulin fraction, which alteration is recognizable by means of various so-called lability reactions. This term is understood to mean reactions which express the fact that the normal colloid stability of the serum is disturbed by reason of a preponderance of the large molecular globulins. Increased serum lability may be manifested in many different ways and may interfere in various seroreactions used for diagnosis, the result being unspecific reactions, that is, reactions that do not express the immunity or the morbid condition which was intended to be demonstrated. Increased serum lability can be ascertained in many different ways. The addition of salt (half saturation with ammonium sulfate) gives a precipitation greater than normal, i. e. the globulin is increased. The rate of sedimentation is