G8 * A PAPER OX EGGS. 



of Northumberland, Durham, and Xewcastlc-upon-Tyne, and 

 especially to the classical series of Mr. John Hancock, who has 

 thus very kindly rendered me much service in the preparation of 

 this paper. 



The colours of eggs fade gradually by exposure to light ; hence 

 the necessity of keeping them in the dark, except when they are 

 required for examination. 



The question now arises, How are the ground colours and the 

 markings on them produced ? 



Before offering a reply it will be necessary to refer to some 

 recognised physiological and other observations bearing on tlie 

 question. 



The colours of the shells of eggs are not found to be different 

 from those which are produced by the blood of mammals and 

 birds, when it has been effused among the living tissues of these 

 creatures, in consequence of a blow having contused the skin and 

 subjacent parts, and ruptured their blood vessels. Such blood, 

 during its gradual disappearance by absoii^tion, gives rise to all 

 the gradations of colour in the solar spectrum. Even in the in- 

 terior of the human body, in the brain itself, similar changes and 

 shades of colour may be observed after death around an old hiv- 

 morrhagic clot that has for months, or even years, been under- 

 going a gradual process of absorption. 



Again, the same colours arc produced, in life, during patholo- 

 gical states of the human mucous membranes. Thus, during se- 

 vere inflammation of the lungs, utenis, kidneys, urethra, and 

 other organs, blood is at times extravasated, and tinges or deeply 

 dyes the mucus or other secretion of tlie part, and as tlie quantitj' 

 of blood that escapes from the capillary network varies much, so 

 the colour of the secretion varies, from the faintest tint of pink, 

 to a red so deep, tliat it appears almost black. 



If the inflammation be intense the colour of the secretion will 

 be ver}' dark red, if less acute, the colour will be paler. In a 

 still less degree there may be, in the case of a serous mcmbrani', 

 a fibrinous plastic elFusion flbrillating and forming a false mem- 

 brane, containing a certain pro])()rtion of blood globules, or none 

 at all. Ill lower degrees still of inflammation the mucus given 



