76. The negligence must be contributory.

In order to establish contributory negligence the defendant has to prove that the claimant's negligence was a cause of the harm1 which he has suffered in consequence of the defendant's negligence2. The question is not who had the last opportunity of avoiding the mischief but whose act caused the harm3. The question must be dealt with broadly and upon common-sense principles. Where a clear line can be drawn, the subsequent negligence is the only one to be considered; however, there are cases in which the two acts come so closely together, and the second act of negligence is so