Here's the relevant quote from Lord Clyde:
"To establish liability by a doctor where departure from normal practice is alleged, three facts require to be established. First of all it must be proved that there is a usual and normal practice; secondly it must be proved that the defender has not adopted that practice; and thirdly (and this is of crucial importance) it must be established that the course the doctor adopted is one which no professional man of ordinary skill would have taken if he had been acting with ordinary care"
Source:
http://www.lemac.co.u...edical_Negligence.htm
You ask "why a case from over 50 years ago can be relevant to present day". That's because Scottish law (as in the rest of UK) isn't determined solely by Parliament. It is also determined by precedents, whereby a higher court has been asked to rule upon the interpretation of statutes (and/or of 'common law'). Once a precedent has been established that precedent, in itself, effectively becomes part of the law. (There may be circumstances where a court can rule that a precedent is no longer valid - e.g. through advances in technology or through changes in society - but unless a specific reason for overturning a precedent can be found, that precedent will always stand). Some precedents are centuries old but they remain as valid, as part of our laws, as on the days when they were determined by the courts.
Chris