Remarks on ihe Physiology of the Egg. 373 
energy may be revived? I must not quit the subject of 
this follicle, without noticing a very curious fact well known 
to every one employed in the concerns of a farm-yard,— 
that, if the obtuse extremity of an egg be perforated with 
the point of the smallest needle, (a stratagem which malice 
not unfrequently suggests,) its generating process is ar- 
rested, and it perishes like the subventaneous egg. Hence 
sir Busick Harwood was Jed to suspect that the elastic fluid 
contained in the air-bag was oxygen, and I was induced to 
examine its nature. Can this curious problem be solved, 
by supposing that the constant ingress of fresh air is too 
highly exciting? A parallel example may be adduced from 
the vegetable kingdom in support of such an opinion. The 
young and tender plant, before it puts forth its roots, is 
often destroyed by having too free a communication with 
the atmosphere, by which its powers are exhausted; it is to 
obviate such an effect, that the horticulturist, taught only 
by experience, covers it with a glass, by which, he limits 
the extent of its atmosphere, and consequently decreases its 
respiration, transpiration, and the inordinate actions which 
would prove fatal to it. 
T shall close this paper with a few observations on the 
formation of the exterior involucrum, or shell, by which 
this microcosm is defended from external violence. We 
here detect a single operation, at once answering two of 
the wisest and most important purposes of the animal: it 
at once averts destruction from the individual, and contri- 
butes essentially to the preservation of its species; for, 
whilst it removes the calcareous matter, which, if allowed 
to accumulate, must render the bird incapable of flight, and 
defeat the best purposes of its existence, it furnishes the 
germ of the future animal with a strong and convenient de- 
fence. The egys of birds are, however, sometimes destitute 
of this provision, which I think may arise from the secre- 
tion of calcareous matter not keeping pace with the exu- 
berant production of the fluids of the egg. Hence we per- 
ceive this imperfection oftener occurring in strong birds, 
and in the months of harvest, when their faod is more 
Juxuriant and abundant. The experiments of Vauquelin, 
which prove that the quantity of calcareous matter voided 
hy birds exceeds that taken in, suggested to Fordyce, that 
birds must require calcareous matter during their laying, 
and that, if the animal be deprived of it, the shell is never 
formed. Such a theory, however, is not only derogatory 
to the wisdom of nature, but illegally deduced from the ex 
periments themselves. Are we to expect, from our imper- 
Aa3 fect 
