110 Dr. Prout on the Changes in the Jixed Principles {Feb. 



. " 1. That the relative weights of the constituent principles of 

 ■ different eggs vary very considerably. 



" 2. That an egg loses about one-sixth of its weight during 

 incubation, a quantity amounting to eight times as much as it 

 loses in the same time under ordinary circumstances. 



" 3. That in the earlier stages of incubation, an interchange of 

 principles takes place between the yelk and a portion of the 

 albumen ; that this interchange is confined on the part of the 

 yelk to a little of its oily matter, which is found mixed with the 

 above-mentioned albumen ; that this portion of albumen under- 

 goes some remarkable changes, and is converted into a sub- 

 stance analogous in its appearance, as well as in some of its 

 properties, to the curd of milk ; and lastly, that a portion of the 

 watery and saline portion of the albumen is found mixed with 

 the yelk, which becomes thus apparently increased in size. 



" 4. That as incubation proceeds, the saline and watery parts 

 again quit the yelk, which is thus reduced to its original bulk ; 

 that in the last week of the process, it undergoes still further 

 diminution in weight, and loses the greater portion of its phos- 

 phorus, which is found in the animal converted into phosphoric 

 acid, and in union with lime, constituting its bony skeleton; and 

 lastly, that this lime does not originally exist in the recent egg, 

 but is derived from some unknown source during the process of 

 incubation." 



Dr. Prout concludes this valuable communication with some 

 remarks on the uses of the yelk, and the apparent generation of 

 earthy matter. The opinion " that the yelk is analogous to the 

 milk of viviparous animals, but more concentrated, and that its 

 chief use is to afford a pabulum to the young animal during incu- 

 bation," is, he says, " corroborated in a striking manner by the 

 present inquiry." 



" With respect to the earthy matter found in the skeleton of 

 the chick when it quits the shell," continues Dr. P. " I think I 

 can venture to assert, after the most patient and attentive inves- 

 tigation, that it does not pre-exist in the recent egg ; certainly 

 not, at least, in any known state. The only possible sources, 

 therefore, whence it can be derived, are from the shell, or trans- 

 mutation from other principles. Whether it be actually derived 

 from the shell, cannot be determined by chemistry ; because, as 

 we have seen, the shells of different eggs differ so much, that the 

 application of averages is out of the question ; and we are of 

 course precluded from ascertaining the exact quantity of lime 

 any particular shell originally contains. There are, however, 

 very strong reasons for believing, that the earthy matter is not 

 derived from the shell. In the first place, the membrana puta- 

 minis never becomes vascular, and seems analogous to the epi- 

 dermis ; hence the lime of the shell, which is exterior to this 

 membrane, is generally considered by physiologists as extra- 



