109 



XVII. — On the Structure of the Animal Basis of the common Egg- 

 shell, and of the Membrane surrounding the Albumen. By 

 William B. Carpenter, M.D. 



, Read October 19, 1842. 



The enclosed preparation consists of some portions of the mem- 

 brane of the egg-shell, decalcified by dilute acid, and of the membrana 

 putaminis. They all have exactly the same structure, and differ only 

 in thickness. The thinnest laminae are seen to possess a beautiful 

 structure, composed of interlacing fibres, between which numerous 

 interspaces are left. I have not been able to ascertain the number of 

 such laminae, which together make up the shell-membrane and the 

 membrana putaminis ; but it must be very considerable. 



The natural uncalcijied membrane of the " egg without shell," pre- 

 sents (as might be expected) exactly the same appearance as the 

 decalcified shell. 



The deposit of calcareous matter probably takes place in the inter- 

 spaces left by the reticulation of the fibres. In the common hen's 

 egg, it certainly has a chalky character. It is so opaque that I have 

 not been able to reduce the shell thin enough to see light through it. 

 It would be interesting to see how far this structure might be modi- 

 fied in those eggs that have been said to have a crystalline fracture ;. 

 (see ' Microscopic Journal,' i. 181). 



The easiest way to obtain a layer of this fibrous membrane, is to 

 put a piece of egg-shell (freed from the membrana putaminis) into 

 dilute acid ; in a short time, a very delicate pellicle may be seen on 

 its internal surface, which may be readily detached. In this layer 

 some bodies may be generally detected, about the size of blood-cor- 

 puscles, and having a granulated appearance when they are seen 

 without the covering of fibrous membrane, which usually renders them 

 indistinct. Some of them may be observed in one of the portions of 

 the enclosed preparation. 



I am strongly inclined to believe, that this membrane is to be re- 

 garded as analogous to the chorion of Mammalia; and that it is formed 

 in the mode in which Dr. Barry has described that membrane to be 

 produced, namely, by the deposition of blood-corpuscles on the ovum 

 from the inner surface of the oviduct ; and the subsequent conversion 

 of these into a fibrous tissue. Dr. Barry (to whom I have shown these 

 preparations) sees his double spiral in some of the fibres ; but this I 

 have not been able to recognize. 



