The densities of positively charged, colloidal iron hydroxide particles binding to the surfaces of glutaraldehyde-fixed cultured Ehrlich ascites tumour cells, were determined on cells maintained in suspension and monolayer cultures. In both cases, there was a higher density of particles bound to the surfaces of microvilli than to the spaces between them. Prior treatment of the cells with ribonu...

We investigate Room squares and subsquares. All terminology is as in [6] and [7], and we will assume the reader is familiar with the definitions contained therein. (These include group-divisible designs, transverial designs, and frames.) We will refer to an incomplete Room square of side s missing a subsquare of side t as an (s, t)-incompZefe Room square. It is known that for any odd t, there i...