“…Cross complement-fixation reactions have been demonstrated between the serum of convalescent herpes zoster cases and the vesicle fluid or crusts of varicella cases, and vice versa, important work in this respect being that of Netter and Urbain (1924) in France and that of R. T. Brain (1933) in this country. Hassko et al (1938) were unable to confirm these findings, and Thomsen (1934) failed to demonstrate any fixation between zoster serum and varicella antigen in 83 cases, the converse reaction with varicella serum and zoster antigen being also negative.…”