314 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



Selmi and Piacentini have lately been prosecuting investiga- 

 tions with the view of ascertaining their relation to animal 

 life. A dog, a pigeon, and a chicken were placed in an air- 

 tight inclosure into which light entered through colored 

 glass. Through one opening air, freed from, carbonic gas, 

 was introduced, and again removed by aspiration. The air 

 used passed through an apparatus for absorbing carbonic acid, 

 the quantity of which was determined after the lapse of some 

 hours. The three animals gave similar results, though not 

 quantitatively alike. The following figures, taken from the 

 observations on the dog, showing the nature of the differ- 

 ences. Taking 100 as the quantity of carbonic acid exhaled 

 by the dog in white light during a certain period: under 

 black glass it was found to be 82.07 ; under violet, 87.73 ; un- 

 der red, 92 ; under blue, 103.77 ; under green, 106.03 ; and un- 

 der yellow, 126.83. With the two birds the differences were 

 still greater. The experiments were very carefully insti- 

 tuted, excluding as much as possible all sources of error, and 

 taking the influence of temperature into account. It is es- 

 pecially interesting to note that the green and yellow rays, 

 which exert the most decided action on plants, are also most 

 favorable to the respiration of animals. 3 C, xxn., 528. 



IKON IN THE BLOOD. 



A French chemist has lately made an examination of the 

 iron contained in the blood and in the food of animals, and 

 finds that this metal is always a component, varying, how- 

 ever, with the animal. Thus, reducing the blood to ashes at 

 a moderately low temperature, the proportion of metallic iron 

 in 100 parts amounted to about 0.051 in man, 0.055 in the ox, 

 0.059 in the pig, 0.037 in the goose, and 0.042 in the frog, show- 

 ing the least percentage in the bird, the next in the reptile, 

 and the greatest amount in the mammal. An important con- 

 clusion from these facts is the necessity of supplying to an- 

 imals generally food containing iron in some assimilable 

 form, as if deprived of this metal the animal must necessarily 

 perish in time, in consequence of the inability to form healthy 

 blood. # 



A similar composition was found to exist in invertebrates ; 

 the blood, whether white or red, always containing an ap- 

 preciable quantity of iron. The general conclusion arrived 



