606 ORGANS OF GENERATION. 



cholesterin or at least the lutein can hardly have a direct influence on 

 the development of the embryo. The egg also seems to contain the 

 mineral bodies necessary for the development of the young animal. 

 The lack of phosphoric acid is compensated by an abundant amount of 

 phosphorized organic substance, and the nucleoalbumin containing iron, 

 from which the hsematogen (see page 598) is formed, is doubtless, as 

 BUNGE claims, of great importance in the formation of the haemoglobin 

 containing iron. The silicic acid, necessary for the development of the 

 feathers, is also found in the egg. 



During the period of incubation the egg loses weight, chiefly due to 

 loss of water. The quantity of solids, especially the fat and the proteins, 

 diminishes, and the egg gives off carbon dioxide, but TANGL disproves 

 the older claim of LIEBERMANN 1 that nitrogen or a nitrogenous substance 

 is given off. On the contrary a corresponding absorption of oxygen 

 takes place, and it is found that during incubation a respiratory exchange 

 of gases occurs. 



As BOHR and HASSELBALCH have shown by exact investigations, the 

 elimination of carbon dioxide is very small in the first days of incubation; 

 on the fourth day the carbon-dioxide production gradually increases, 

 and after the ninth day it augments in the same proportion as the weight 

 of the foetus. Calculated upon 1 kilogram weight for one hour it is, 

 from the ninth day on, about the same as in the full-grown hen. HASSEL- 

 BALCH 2 has also shown that the fertilized hen's egg not only gives off 

 nitrogen the first five or six hours of incubation, but also some oxygen, 

 and that we are here dealing with an oxygen production which runs 

 parallel with the cell-division. It is not known whether this oxygen 

 formation connected with the life of the cell is a fermentative or a 

 so-called vital process. 



While the quantity of dry substance in the egg during this period 

 always decreases, the quantity of mineral bodies, protein, and fat always 

 increases in the embryo. The increase in the amount of fat in the 

 embryo depends, in great part upon a taking up of the nutritive yolk 

 in the abdominal cavity. The weight of the shell and the quantity 

 of lime-salts contained therein does not remain unchanged, according 

 to the recent investigations of TANGL. S The egg-shell (lime shell and 

 shell membrane) of a hen's egg weighing 60 grams loses (calculated 

 on the dry) during incubation about 0.4 gram, of which 0.15 gram is 

 calcium and 0.2 gram is organic substance. 



Very complete and careful chemical investigation on the development 



1 Tangl and v. Mituch, Pfliiger's Arch., 121; Liebermann, ibid., 43. 



2 Bohr and Hasselbalch, Maly's Jahresber., 29; Hasselbalch, Skand. Arch. f. 

 Physiol., 13. 



3 Tangl with Hammerschlag, Pfliiger's Arch., 121. 



