John Aitken's chain saw

摘要

Childbirth in the 18th century was fraught with hazards, especially for dwarfs and women of small stature, often afflicted with pelvic deformity due to rickets – a problem in Britain until the mid-20th century. For contracted antero-posterior diameter of the pelvis, obstructed labour might end in the death of the child whilst extraction with instruments or caesarean section held a high death rate for the mother. Thus, division of the symphysis pubis to gain room for a natural birth with survival of mother and child was suggested. First performed successfully in Paris, in 1777, J Sigault sectioned the cartilage of the symphysis with a knife.1 Others were less fortunate as the symphysis was often ossified, for which, in 1785, John Aitken (c. 1745–90) introduced a flexible saw based on a watch chain (Figure 1) with teeth to cut from inside outwards.2 Unfortunately, both knife and saw often injured the urethra and bladder, and symphysiotomy never became popular. Later, Aitken's saw was adapted successfully for bone section, particularly joint excision, followed by its mechanisation to cut on the outside of an endless chain. Sadly its hand-powered speed proved inadequate to cut compact bone expeditiously. Nevertheless, this concept was the eventual source of today's successful chain saw of the timber industry.3