Letter from Howard Walter Florey to J F Boyd, Pathology Department, Western Infirmary, Glasgow Apologises for delay in answering Boyd's interesting letter - agrees that endothelial cells are probably coming off and in some way the defect is made good - comments on the difficulty of finding mitotic figures in normal endothelium - thinks Boyd may be right in thinking that endothelial cells are damaged by "toxins" which circulate in blood but this is difficult to prove. 21 December 1960