EGGS OF FOWLS. 451 



mal matter, sulphuric acid, phosphoric acid, chlorine, and alkali, 

 lime and magnesia, and carbonates of lim i and magnesia ; in 

 fact, of all the fixed principles found to exist in the egg. But 

 the carbonate of lime is most abundant, and is obtained by eva- 

 poration in the form of a white powder.* 



It is well known that when the egg is kept at a temperature 

 of about 100 by the warmth of the mother, or by any other ar- 

 tificial means for three weeks, a chicken is formed in it, which, 

 at the end of that period, breaks the shell. Dr Prout made a 

 number o ' t xperiments to determine the changes which take place 

 in the constituents of . the egg during the period of incubation, f 

 The following is a summary of these experiments : 



If we suppose the original weight of the egg to be 1000 grains^ 

 it will be found that, after a week's incubation, the average loss 

 is about fifty grains. The following table shows the amount of 

 the various constituents of the egg on the eighth day of incu- 



bation in two different eggs : 



No. 1. No. 2. 



Grains. Grains. 



Unchanged albumen, . 232-8 . 247'1 

 Modified albumen, . , 



Liquor amnii, membranes, ~i 97 A 9 



blood-vessels, &c. f 

 Animal, . . . 22'0 I 



Yolk, .... 301-3 . 324-5 

 Shell and loss, . 167-1 . 153-2 



1000-0 1000-0 



As soon as the process of incubation has commenced the yolk 

 becomes more fluid than usual ; the liquor amnii increases, and 

 that portion of the albumen occupying the upper and larger end 

 of the egg begins to assume a peculiar aspect. When the 

 egg is boiled it puts on an appearance somewhat resembling 

 that of curds-and-whey. It has a yellow colour, and contains a 

 portion of the oil of the yolk. Hence it would appear that a por- 

 tion of the oil of the yolk must in some unknown way pass into 

 that part' of the albumen. It is this portion of the albumen 

 which, in the preceding table, is distinguished by the name of 

 modified albumen. The yolk at this period has become more 



* Prout, Phil. Trans. 1822, p. 380. f Ibid. p. 388. 



