44 ON THE INCUBATED EGG. 



cerated them for two days in albumen, until they were thoroughly satu- 

 rated, and so soft and pulpy that I could readily apply them to the egg, 

 and bring the edges so well together, that the joining was scarcely ob- 

 servable. After having covered the eggs in this way, and allowed them 

 to dry, I repeated the papering and varnishing four times ; taking care 

 to bring the middle of each section opposite the joining in the previous 

 coating. They were now covered with four thicknesses of paper, satu- 

 rated as described ; besides very numerous coatings of albumen, used as 

 a varnish, first on the shell, and subsequently between each layer of pa- 

 per ; the whole forming a covering so thick and horny, that I felt con- 

 vinced it was entirely impermeable." 



The eggs thus protected were submitted to incubation on the llth of 

 April, and such of them as were examined during different periods of the 

 process exhibited the development of the embryo without any deviation 

 from its normal condition, the chick arriving at maturity in the same 

 time as when placed under ordinary circumstances. To render the ex- 

 periment doubly sure, it was afterwards repeated, and attended with a 

 similar result, though in addition to the covering already described, there 

 were added several coatings of oil-paint, purposely prepared with the most 

 noxious materials, as a test of the air-proof nature of the protection used 

 in the first instance. 



Another observation of importance recorded by Mr. Town, is that upon 

 his removing a large portion of the shell without injury to the chorion, 

 while circulation wa5 going forward, no visible eflfect was produced on 

 the blood by the admission of atmospheric air. 



" The blood still continued to leave the chick of a livid-red or venous 

 colour, pass to the chorion, and, after having circulated through that 

 membrane, was returned to the chick of a bright scarlet ; and this dif- 

 ference remained perfectly apparent so long as the circulation continued ; 

 and then, but not until then, the atmosphere appeared to act upon the 

 blood ; and both arteries and veins became alike bright scarlet, as if 

 this change were effected by circulating through the chorion, and de- 

 pended on some principle of vitality." 



It appears to us that Mr. Town's first experiment might be advanta- 

 geously varied by placing the egg in a condition under which the possi- 

 ble access of atmospheric air would be even still more effectually guarded 

 against. It might, for instance, protected in the way he has describ- 

 ed, — be immersed in mercury, — and then subjected, in an hermetically- 

 sealed vessel, to the temperature under which artificial incubation is 

 known to be produced. The development of the embryo under these 

 circumstances, even though the experiments already performed may be 



