The degree of relationship by blood between a person and his lineal relative by blood shall be determined by counting the number of generations upwards or downwards from himself [as the case may be], one generation being taken as one degree. As between the person and his collateral relative, the degree of relationship shall be determined by the total number of generations counting upwards from himself to the common lineal ancestor and then from such common ancestor downwards to the relative by blood with whom the degree of relationship is to be determined.