All of 37 cold haemagglutinins isolated from sera of patients with chronic cold haemagglutinin syndrome were shown to contain k chains only. When data obtained from other investigators are added, it appears that a total of at least 59 isolated cold haemagglutinins have been found to contain only type K γM‐globulin molecules. In analogy with current views on the structure of the γG‐globulin molecule, it is suggested that each active site of the cold haemagglutinin molecules is made up by a close interaction of the heavy and light polypeptide chains. It is further suggested that the characteristic behaviour of cold haemagglutinins with regard to serological specificity and/or thermal amplitude is only compatible with relatively small structural variations of the light chains within the limits imposed by k chains.

IN the last century, Meltzer and Welch (1884) had already noticed haeniolysis of erythrocytcs of oxen caused by mechanical trauma. Later, Rous aiid Turner (19 16) investigated erythrocytes of shecp arid dogs and found the resistance to shaking to bc quite unrelated to osmotic rcsistancc. These findtngs, howevcr, drew no further attention until 1944, when Slien, Castle aiid Fleming considered this phcnomcnon of mechanical haemolysis again and described a quantitative method for its mcasuremcnt. They observcd an cnhanced mechanical fragility of erythrocytcs in congenital haemolytic jaundice (hcrcditary sphcrocytosis) and the test was introduced into clinical laboratorics for the &fferential diagnosis of haemolytic disorders. Sincc thcn the method has becn modified by Young (1947), Maicr (I~so), Matthes (rgjo), Gardner, McElfrcsh, Harris and Diamond (1951)~ Tolentino ( I 95