Letter signed by Dr Russell Brain, 19 Jan 1931. Circular from Birth Control Investigation Committee (BCIC), 1931. Dr John R Baker's Test of Bircon, 1931. Request for help for doctors on 'dutch cap technique', 1934. Request for test of Bircon with human sperm; Dr Baker's reply, 1935. Testing of rubber and dating sheath: Dr E Elkan (National Birth Control Association (NBCA) Medical committee] and Dr Schidrowitz, 1936. Correspondence re early formula for Bircon, 1936. Latex protectives omitted from Approved List: possibility of slandering London Rubber Co, Nov 1937. Tests of Bircon with human sperm, 1937. Use of formaldehyde in solution in Durol: test by Dr H M Carleton, Oxford, 1937. Advertisements and notices by London Rubber Co mentioning NBCA, ''should not be allowed'', 1938. Confusion over nomenclature: Durex, Paragan, Ona, protectives and sheaths. Subscription to FPA offered by London Rubber Co, but ''cheque returned'', March 1939. Refusal of membership of FPA to London Rubber Co, May 1939. Removal of sheaths and condoms from Approved List, over question of dating, May 1940.