It has already been described of that the vitamin B12 content in natural water varies with the conditions of sampling the water to be analyzed, such as the season of year, the time of day and the depth of water, etc. Since said variation is though, to have distorted the data thus far published about vitamin B12 content in natural water, a few confirmatory researches were made on this item, the following results being obtained.
(1) When samples of natural water (sea-water, river-water and drain-water) were separately placed in vases and kept in a dark place, B12's in these samples increased, attaining to their maximum contents likewise in 2 or 3 days and decreasing afterwards (see Table 1). This is a general tendency and may perhaps be attributed to the work of bacteria originally contained in the sample waters.
(2) Samples taken from upper layers (0-50m in depth) of the water of Lake Ikeda, when kept in the conditions the same as those under which the above samples were stored, uniformly showed noticeable changes of vitamin B12 contents in first 7 days, while samples taken from deeper layers of said source (deeper than 50m) showed increases of B12 only in first one day and decreased after that time to stational values which were not always strictly constant (see Table 3).
(3) In order to confirm the decomposition degree of B12 in sea-water by sun-light, the B12 solution was put into a polyethylene bag, and the bag was suspended for about 10 hours at different depth-layers of the sea (Dec. 5, 1958) with the following results shown in Fig.
1. In a nutshell, at the surface layer (0-20m) a considerable loss of B12 was to be seen, while at the depth of 30m or more than that, hardly any was. Hereby it seems quite necessary for any researcher who attempts to examine B12 content or to make water-sampling of it that he should take the loss of B12 by sunlight effects into consideration.