Safety of live oral poliovirus vaccine and the origin of HIV infection in man.

The beam splitter comprises first and second prisms having diagonal surfaces placed together in juxtaposed relationship with means on the opposing edge portions of the surfaces holding the surfaces in spaced relationship to define a thin chamber therebetween. A fluorinated hydro-carbon liquid fills this chamber and one diagonal surface is provided with a multi-layered di-electric coating. High reflectance is provided for the S component of a laser beam and high transmittance for the P component for both ruby and neodymium laser wave lengths of 0.694 and 1.06 microns respectively. The use of the liquid interface avoids the necessity of cement or glue to hold the prisms together so that the beam splitter may be used with high power laser beams without the risk of deterioration.