Nitrate film was last made around 1950 so your negatives are at least 60 years old. They have survived this long without any special care. I really wouldn't worry but would get them copied as soon as possible. I would suggest copy negatives rather than scanning them. This is based on all the bad scans that appear on APUG and other web sites .If the images are important to you I would recommend that you avail yourself of a professional conservator rather than doing the job yourself.