312 Proceedings of Royal Society of Edinburgh. [may 7, 
Another laying hen was killed, but in this case the amount of 
lime found was less than in the first case. 
These results were obtained during February and March, when 
the ground was either frozen or covered with snow (or both), and 
this no doubt was the cause of the small proportion of calcareous 
matter in the gizzard of the two hens referred to, as at the same 
time true shell-less eggs were being laid by hens having liberty to 
feed on any form of lime within their reach in the fields. 
We have since found that birds in favourable circumstances may 
store enough calcareous matter to serve for the formation of the 
shells of two or three eggs, ^.e., should they have plenty of cal- 
careous gravel, they have storage power in the crop and gizzard to 
this extent. But it is evident that birds do not possess storage 
power for carbonate of lime to any extent beyond this. When 
totally deprived of it, they either cease to lay eggs or lay them 
without shells. This we proved by shutting up two other hens, 
precautions being taken that they were deprived of all lime except 
that naturally in their food; the result being, that they ceased 
laying after each had laid three eggs, the carbonate of lime in which 
amounted to not more than 130 grains. Thereafter they had 
sulphate of lime given with their food, and after six days they 
began to lay eggs with carbonate of lime shells. 
On examining the oviduct of one of the hens fed on calcium 
sulphate, at the conclusion of the experiments, its thick-walled part 
was found to be secreting lime, apparently the carbonate, in con- 
siderable quantity; both the lining epithelium of the secreting 
follicles and the superficial epithelial layer containing lime in the 
form of minute granules, which, incorporated with the organic 
matter, appear to form the egg shell. 
It is interesting to note in this connection that the epithelial cells 
are evidently in a state of great functional activity, as a consequence 
of which the nucleus is considerably obscured, and that along with 
the lime there is secreted some other substance (probably the 
organic material in which the lime is eventually embedded). 
In the process of digestion, mineral compounds pass from the 
alimentary canal very directly, and but little altered, into the blood- 
vessels and lymphatics ; but it must be remembered that ordinary 
chemical changes take place in the alimentary canal, and, in the 
