. Annals of applied biology. Biology, Economic; Biochemistry. H. G. Thornton 261 acid. This explains the fact, observed by Conn (3), that on Lipman and Brown's peptone agar, "overgrowths are often so to inter- fere with counting and prevent the isolation of pure cultures from the colonies," and also that these overgrowths are reduced on his medium containing ammonium phosphate and sodium asparaginate. On the tyrosine medium scarcely any growth took place. It appears that this is due, not to any inhibiting action of the tyrosine, but to the inability of the organism to m
. Annals of applied biology. Biology, Economic; Biochemistry. H. G. Thornton 261 acid. This explains the fact, observed by Conn (3), that on Lipman and Brown's peptone agar, "overgrowths are often so to inter- fere with counting and prevent the isolation of pure cultures from the colonies," and also that these overgrowths are reduced on his medium containing ammonium phosphate and sodium asparaginate. On the tyrosine medium scarcely any growth took place. It appears that this is due, not to any inhibiting action of the tyrosine, but to the inability of the organism to make full use of the tyrosine molecule in its nutrition. This is shown in the following experiment, in which the 80 70 60 ^ 50 a 40 30 20 10 -. Tyrosine + Asparagine Asparagine • Tyrosine 2 3 4 5 6 Days growth. Fig. 8. B. dendroides. Effect on tyi'osine and asparagine on the spreading growth. growth was compared on media similar to those tested in the last experiment but having organic nitrogen supplied as follows: A. 0-12 per cent, tyrosine. B. 0-12 per cent, tyrosine + 0-05 per cent, asparagine. C. 0-05 per cent, asparagine. The test was conducted in a manner similar to the last experiment except that the plates were incubated at 25° C. to accelerate the growth. The curves (Fig. 8) show the mean areas of growth, measured at intervals, of ten parallel platings in the case of media B and C and of seven parallel platings in the case of medium A. It will be seen that in the presence of asparagine, tyrosine does not check but slightly stimu- lates the growth, whereas with tyrosine alone the growth is very slight. Tests made with the tyrosine medium, however, showed that it was. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Association of Applied Biologists; Association of Economic Biologists. [Wellesbourne,
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