ON THE INCUBATED EGG. 43 



tlie bird in ovo, which are well worthy the attention of those of our read- 

 ers who may pursue the subject of Animal Physiology. It appears that 

 the anatomical modeller to the Hospital, — Mr. Joseph Town, — whose 

 high talent in his profession has so largely contributed to the celebrity of 

 the Museum in that establishment, received instructions from the trea- 

 surer, — Mr. Harrison, — to prepare a series of models illustrative of the 

 changes which occur in the egg during the period of incubation. Before 

 however commencing his task, he consulted the works of Sir Everard 

 Home and other writers, that he might render himself familiar with the 

 opinions of previous observers, and see how far his own observations would 

 tally with the views entertained in reference to this subject, by physiolo- 

 gists of the present day. The result was, that in the very outset of his 

 undertaking, his attention was drawn to a circumstance which seemed 

 to oppose the generally-received theory of the decarbonization of the 

 blood in the embryo, by its contact with the oxygen of the atmosphere ; 

 and this induced him to institute a series of experiments, which convey 

 the startling announcement, that the natural development of the contain- 

 ed embryo goes forward and is perfected without the transmission of at- 

 mospheric air to arterialize the venous circulation. 



The lining membrane of the shell, through which the air was supposed 

 to pass before reaching the chorion, was remarked by Mr. Town to in- 

 crease in density, and become apparently less permeable to air, in a ratio 

 corresponding to the extent of time during which the process of incuba- 

 tion had gone forward, a condition directly opposed to that which might have 

 been expected to obtain, assuming the correctness of the above-mention- 

 ed theory of decarbonization. It then occurred to Mr. Town, that in the 

 cases in which it had been found that incubation did not go forward 

 when a barrier was put to the supposed egress of atmospheric air, that a 

 source of fallacy might have been present, in the employment of a sub- 

 stance to protect the shell, which, from its noxious qualities had been 

 fatal to the existence of the contained embryo. Having determined to 

 satisfy himself on this point, Mr. Town infonus us that he repeated the 

 experiment in question in the following manner. — 



" Having selected a number of fresh eggs, as nearly as I could of the 

 same size and form, I varnished them over, many times, with albumen, 

 which had been allowed to stand for some time in an open vessel, until, 

 by evaporation, it had acquired considerable consistence : this was re- 

 peated until the shells appeared completely lackered. I then, with a 

 pencil, marked one of them into equal sections, like the divisions in an 

 orange, and cut a piece of card to correspond exactly with one of these 

 divisions ; then a great number of papers similar to this card ; and ma- 



