an obsolete term for the relative retardation in loss of viscosity of a solution of casein incubated with trypsin, to which a drop of abnormal blood serum (as from a cancerous patient) has been added, compared with that in a similar solution to which normal serum has been added; if the former drips through the tube of the viscosimeter in 100 seconds, and the latter in 104 seconds, the antitryptic index is 4.