The 1973 Trojan survey of a region close to the preceding Lagrangian point is discussed in this paper. This region consists of four overlapping fields and one field for the photometric calibration, centered on Selected Area 68. Orbital elements of most of the 1504 asteroids found have been published in the Minor Planet Circulars. Among these are 5 Hungaria-type asteroids, 12 of the Hilda type and 55 Trojans. The accuracy of the orbits is somewhat lower than in the Palomar-Leiden survey of 1960, because of the shorter arc in the present investigation. A discussion of the degree of completeness of this material shows that the (photographic) magnitude interval 19.5-20.0 is only 50% complete; to obtain completeness down to magnitude 20.0 the number of found Trojans brighter than this limit has to be increased by 9. In combination with the surveys of 1960 and 1965 an improved distribution of the number of Trojans as a function of distance to the preceding Lagrangian point (L4) has been constructed. A preliminary discussion, including the result on L5, yields a value of 2.0 for the ratio of Trojans around L4 and L5, along the ecliptic. The L5 Trojans appear to be deficient in orbits of small inclination. Taking this into account we find this ratio again to be 2.0 for the total Trojan clouds around L4 and L5. Possibly, however, high-inclination Trojans were systematically overlooked in this survey. If this would be true, the ratio N(L4)/ N(L5) is increased to 2.3. The uncertainty of these numbers can be estimated to be ±0.5.