RESEARCH work can be divided generally into two main classes, firstly that of a purely academic nature and secondly the investigation of a practical problem with the object of producing data to solve this problem. Each of these classes has its part to play in the acquisition of knowledge and it often occurs that work done from the purely academic standpoint is of great assistance to the person endeavouring to produce data to solve a practical problem. W. T, Marshall and N. R. Tembe