tubes were then prepared, each containing I c.c. of the enzyme sol. and 5 c.c. of the substrate. The tubes were incubated at o° C. for periods differing between o min. and 96 hr., then were held at 40° C., and the time required at the latter temp. for the production of a coagulum was noted, with the following results:

In the last experiment of this series-held at o° C. for 96 hr.the flocculent precipitate was so finely divided that the period of time required for its separation at 40° C. was determined with difficulty.

Another series of experiments was carried out as described above, with the single exception that the temp. of mixing the rennin and the milk, and of the preliminary holding, was 15° C. In these experiments the transformation of the casein into paracasein proceeded more rapidly than at oo C., and consequently less time was required for the separation of a visible precipitate. For instance, after holding at 15° C. for periods of o, 10 and 30 min., the coagula were formed at 40° C. after 6 min., 21⁄2 min., and 55 sec., respectively; while after 45 min. at 15° C. coagulation had already occurred.

Müller concludes that rennin exerts its characteristic action, to a certain degree, at oo C.

4. Summary. The power to survive prolonged exposure to low temp. is possessed by various enzymes, including those producing hydrolysis of fats, carbohydrates, and proteins; those concerned in biochemical oxidations and reductions; the clotting enzymes; and that of alcoholic fermentation. The enzymes retain their catalytic power after exposure, either in situ or in solution in vitro, to temp. varying from a few degrees above oo C. to the temp. of liquid air (- 180 to — 191° C.). The shortest periods of holding-invariably less than I day and usually less than I hr.were at the temp. of liquid air. The longest period of holding was 89 mo. at a temp of - 9.4° to - 12.2° C.

The activity of certain of these enzymes, including rennin, zymase, and those hydrolyzing fats, carbohydrates and proteins, has been studied at low temp., varying from that of an ice box to one of -9° to - 12° C. While the enzymes induce autolytic digestion, or act on artificial media, at these temp., the velocities of their reactions are always diminished to a considerable degree.

1. KASTLE and LOEVENHART: Amer. Chem. Journ., 1900, xxiv, p.

491.

2. PENNINGTON and HEPBURN: Journ. Amer. Chem. Soc., 1912, xxxiv, p. 210; U. S. Dep't of Agri., Bur. of Chem., Circular 75, 1911.

3. PENNINGTON and ROBERTSON: U. S. Dep't of Agri., Bureau of Chem., Circular 104, 1912.

4. KOVCHOFF: Ber. d. deutsch. botan. Gesellschaft, 1907, xxv, p. 4735. POZERSKI: Compt. rend. de la soc. de biol., 1900, lii, p. 714.

6. CHANOZ and DOYON: Compt. rend. de la soc. de biol., 1900, lii,

P. 453.

7. BUCHNER: Die Zymasegährung. München und Berlin. Druck

und Verlag von R. Oldenbourg, 1903, pp. 67, 226.

8. AHRENS: Zeitschr, f. angewandte Chem., 1900, 483.

9. MACFADYEN: Proc. Royal Soc. of London, 1900, 1xvi, p. 180;

Lancet, 1900, lxxviii (1), p. 849.

10. PENNINGTON, HEPBURN, ST. JOHN, WITMER, STAFFORD and

BURRELL: Journ. Biol. Chem., 1913, xvi, p. 331.

11. HEPBURN: U. S. Dep't of Agri., Bureau of Chem., Circular 103, 1912, p. 6.

12. VAN DRIEST: Third Int. Congr. of Refrig., 3d Sec. (Netherlands). Notes on the investigation of preserving fish by artificial cold; prelim. report, 1913, p. 30.

13. RICHARDSON : Premier Congrès Internat. du Froid, 1908, ii, p. 261. 14. PENNINGTON and HEPBURN: U. S. Dep't of Agri., Bureau of Chem., Circular 103, 1912, p. 1.

15. MÜLLER: Arch. f. Hygiene, 1903, xlvii, p. 127.

16. BUCHNER: Ber. d. deutsch. chem. Gesellschaft, 1897, xxx, p. 117.

17. MURISIER and FICK: Verhandlungen der physikal.-med. Gesell

schaft, Würzburg, 1873, iv, p. 120.

18. HOPPE-SEYLER: Arch. f. d. gesammte Physiol., 1877, xiv, p. 395.

19. FLAUM: Zeitschr. f. Biol., 1891, xxviii, p. 433.

20. OGURO: Biochem. Zeitschr., 1909, xxii, p. 278.

21. BABCOCK: Second Intern. Congr. of Refrig., English Edition of

the Rep. and Proc., 1910, p. 430.

22. BABCOCK, RUSSELL, VIVIAN and BAER: Eighteenth Ann. Rep.,

Agr. Exp. Sta., Univ. of Wis., 1901, p. 136.

23. RAVENEL, HASTINGS and HAMMER: Journ. Inf. Diseases, 1910, vii, p. 38.

24. SELMI: Ber. d. deutsch. chem. Gesellschaft, 1874, vii, p. 1463.

25. CAMUS and GLEY: Arch. de physiol. norm. et path., 1897, (V)

ix, p. 810.

26. MORGENROTH: Arch. intern. de pharmacodynamie et de therapie, 1900, vii, p. 272.

27. VAN SLYKE: Journ. Biol. Chem., 1914, xix, p. 174.

PLANT PIGMENTS

The chemistry of plant pigments other than chlorophyll1 CLARENCE J. WEST

Accompanying chlorophyll in the chloroplasts of green plants and leaves there are two yellow pigments, carotin and xanthophyll. Isomers of each of these have been found in lycopin, the coloring matter of the tomato; and lutein, the pigment found in the yolk of eggs. Fucoxanthin, a xanthophyll-like substance, found in brown algae, has also been described.

The principal result of the studies thus far made upon these pigments is that a satisfactory method for their isolation and purification has been worked out. Very little if anything is known concerning their constitution. Owing to the difficulty of obtaining them in large quantities, to their ease of oxidation during the process of purification, and to the fact that upon decomposition they yield only amorphous products, it may be a long time before their constitution is established.

Carotin. Carotin is widely distributed, being generally associated with chlorophyll in the chloroplasts. It is also found in various parts of many plants. The color of yellow or orange petals is frequently due to it, e. g., the corona of the common narcissus. It is largely responsible for the color of the carrot root, being present as innumerable small intracellular crystals. The tint of many fruits is due to amorphous granules of carotin.

The most recent chemical study of carotin has been made by Willstätter, who isolated it from the leaves of stinging nettle and from carrots, and showed the complete identity of the two preparations. The following methods were used: 100 k. of dry leaves were extracted with 120 1. of petroleum ether (b. p. 40°-70°) in the cold for two days, the extract filtered off and the residue washed with 60 1. of petroleum ether. The extract was shaken with a little conc. alcoholic potash sol. to remove chlorophyll, then with water, concentrated to about 3 1. and allowed to crystallize. After shaking with I 1. of low-boiling petroleum ether, the product was purified by repeated precipitation from carbon disulfid sol. with absolute alcohol. Finally it was recrystallized from petroleum ether (b. p. 30°-50°). The yield was 3.1 gm.-0.03 gm. per k. of dry leaves.

Modifications of the above method, in which mother liquors from the preparation of chlorophyll were used, are given by Willstätter and Stoll. The carotin was found in the petroleum ether