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The tube method of microbiological assay of vitamin B,, with Lactobncilliis Zeichnzaitnii 31 3, as described by Emery, Lees and Tootill, has been adapted for routine use in a laboratorj-where demands for the assay are only intermittent.The vitamin B,, potency has been given for a number of materials used in the compounding trade ;LS determined by this test.~C H E A S I S G interest in vitamin B,, has led the provender milling trade to denialid that the potency of concentrates purporting to be rich in this factor should be stated. Analytical and consulting laboratories therefore require a rapid and reliable method of estimation that can be brought into use arid laid aside according to need. The microbiological technique will fulfil this purpose if it can be so modified that not too much time and space of a busy and crowded laboratory need be taken up with maintaining culture and medium between tests. CHOICE OF METHODConsideration of the methods of microbiological assay already in use led to the conclusion that a tube method, rather than a plate method, lent itself most readily to work in the routine laboratory. Either Lactobncillzis lactis Dorner or L. Zeiclzmaitiiii 313 could be used as the test orginism, but discussion with Dr. E. Lester Smith and Dt. IV. F. J. Cuthbertson, of Glaxo Laboratories Ltd., indicated that the latter organism was the one of choice.The niethod of assay eventually established as routine was that of Emery, Lees and 'Tootil1,l with such modifications as were necessary when the method was needed for occasional use only.TEST OIIGASISM Tlic first cultures of L. Zeichmniiiiii 313 used in the tests were obtained through Dr.Cuthbertson ; the>, were freeze-dried cultures or organisms grown in the special milk medium described below. As the requirements were intennittent and a period of two or three weeks would sometimes elapse between tests, it was thought that the properties of the organism might be upset by the daily transfer sj-stem because of contamination or other accidents. PRITCHARD: EXPERIENCES WITH THE MICROBIOLOGICAL ASSAY OF[VOl. 76 fresh tomatoes were used. No difficulty has been met in getting supplies of fresh tomatoes during the last twelve months, but several tins of tomato juice were kept as a stand-by. Several brands were found to be suitable. The juice was prepared just before it was needed. The tomatoes were immersed in boiling water for a few minutes and then skinned. The skinned fruits were placed in a piece of cloth and the juice was expressed after mashing them. The juice was then mixed with kieselguhr and filtered with suction through a Whatman No. 1 filter-paper supported on a No. 54.After incubation at 37" C for 24 hours, the contents of the vial containing the actively growing organism were solid except for about 0.5 ml of clear yellow liquid, which rested on the surface of the clot. To effect the daily transfer, 0 6 m l of the mixed contents of the vial was removed with a sterile pipette and p1act:d in a fresh bottle of medium, which was then incubated in the same way...

2.Over the range 5-50 pg. of hydroxyproline/ml. (i.e. per 10 ml. of coloured solution) reasonable agreement was obtained on any one occasion between the densities of coloured solutions developed from aliquots of the same standard solution, and a smooth curve resulted when colour density was plotted against concentration. Nevertheless, from time to time the level of the standard curve fluctuated a little, and therefore it is advisable to include three standard solutions with each set of ' unknowns I , as recommended by Neuman & Logan.3 . The density of the coloured solution developed from hydroxyproline was affected: (a) by variation in the concentration of copper sulphate, (b) by variation in the concentration of hydrogen peroxide, (c) by the presence of amino-acids other than hydroxyproline. When the concentration of copper sulphate was increased from O~O I M . to 0.05~. the density of colour given by hydroxyproline alone was scarcely affected, but in the presence of other amino-acids an appreciable increase in colour density resulted.When the concentration of hydrogen peroxide used was reduced from 6y0 to zyo, a marked increase in colour density was noted for solutions of hydroxyproline alone, but when other amino-acids were present-the increase was less.When other amino-acids (as a mixture or in the form of protein hydrolysate) were present in the ratio of amino-acid to hydroxyproline of 8 to I, the colour density was not affected ; a slight decrease in colour density was noted at a ratio of 50 to I, which became more marked at ratios of IOO to I and 1200 to I. Samples of standard white fish meal. typical of t h a t produced on a large scale for animal feeding in this country, have been tested for their content of eight members of the vitamin-B complex and t h e average figures obtained compared with those widely scattered throughout the literature. I t was found t h a t white fish meal will supply, to rations for animal feeding, significant quantities of t h e known members of the vitamin-B group, in addition t o protein of high biological value.

Whale‐meat and ‐liver meals, long used in animal feeding‐stuffs as protein‐source, also contain B vitamins. Samples representing 1950–51 season's production of two British whaling companies operating from Great Britain have been examined for six members of the vitamin‐B complex by microbiological methods. The results, compared with those obtained on other feeding stuffs and with published figures, indicate that whale‐meat meal is similar to ordinary meat meal, but whale‐liver meal is very rich in these factors. Examination of animal requirements indicates that both products would make a substantial contribution to the daily vitamin‐B needs of farm stock.