652 



SCIENCE 



[N. S. Vol. XLIV. No. 1140 



On page 175 of Director Thome's excellent nessee Station before accepting Wheeler's con- 

 book on " Farm Manures," he also shows that, fidential report of Mooers' personal opinion. 



ACRE- YIELDS IN OHIO MANURE-PHOSPHATE EXPERIMENTS: AVERAGE OF 9 TEARS, 1906-1914 



when the increase is computed by the method 

 which he states " has been deemed best," the 

 net profit is greater per acre, and very much 

 greater per dollar invested, from raw rock 

 phosphate than from acid phosphate. 



The accompanying table gives the average 

 of the actual yields secured in these Ohio ex- 

 periments during the last half of the eighteen- 

 year period. 



If we value the corn at 40 cents a bushel, the 

 wheat at 80 cents, and the hay at $8 a ton, and 

 count the cost of rock phosphate at $7.50 per 

 ton and acid phosphate at $15, we find, by this 

 direct method of computation, that the rock 

 phosphate was slightly more profitable per acre, 

 and more than twice as profitable per dollar in- 

 vested, as the acid phosphate. 



In his letter to the agricultural editors, 

 Dr. Wheeler quotes a personal letter from 

 Professor Mooers expressing his opinion as to 

 the conclusions which should be drawn from 

 experimental data, in part unpublished, secured 

 by the Tennessee Experiment Station. If this 

 opinion is based upon a continuation of the 

 experiments in which two crops (wheat fol- 

 lowed by cowpeas) were grown every year on 

 the same land, as reported in Tennessee Ex- 

 periment Station Bulletin No. 90, in which on 

 page 89 it is shown that for each dollar in- 

 vested rock phosphate paid back $2.29, and 

 steamed bone meal only $1.90, and in which the 

 use of steamed bone meal is commended and 

 the use of rock phosphate discouraged, we 

 must await further publication by the Ten- 



Eor more complete data from the phosphate 

 experiments conducted by many state experi- 

 ment stations, the interested reader is referred 

 to Illinois Experiment Station Circular 186, 

 " Phosphates and Honesty." 



Cyril G. Hopkins, 

 Albert L. Whiting 

 University op Illinois 



SPECIAL ARTICLES 



THE LIGHT-PRODUCING SUBSTANCES, PHOTO- 



GENIN AND PHOTOPHELEIN, OF 



LUMINOUS ANIMALS 



In a previous issue of Scojnce (IN". S., 

 XLIV., 208, 1916), I called attention to 

 Dubois's discovery of substances called luci- 

 ferin and luciferase in the West Indian 

 " cucullo " Pyrophorus noctilucans, and the 

 mollusc, Pholas dactylus. I also recorded the 

 existence of similar bodies in the fire-flies, 

 Photinus and Photuris, and of luciferin in 

 luminous bacteria. Luciferase, according to 

 Dubois, a thermolabile enzyme capable of ac- 

 celerating the oxidation of luciferin, is pre- 

 pared by allowing an extract of luminous cells 

 to stand until the light disappears. The luci- 

 ferin is thus completely oxidized and used up. 

 The luciferin, according to Dubois, a thermo- 

 stabile substance capable of oxidation with 

 light production, is prepared by extracting the 

 luminous cells with hot water which destroys 

 the luciferase but not the luciferin. Light 

 will appear if we mix the solutions of luciferin 

 and luciferase in presence of oxygen. Each 



