358 Dr, Paris on the Fhysiology of the Egg. [May, 



tians, however, by a nice adjustment of their ovens, or mamah^- as 

 they are called, succeed in hatching a great proportion of the 

 eggs entrusted to their care by artificial heat. The celebrated 

 Reaumur introduced the method into France; and Sir James 

 Hall invented a regulating stove by which an equable tempera- 

 ture might be easily procured for the same purpose. During the 

 period that 1 was at college, the late Sir Busick Harwood, the 

 ingenious Professor of Anatomy in the University of Cambridge, 

 frequently attempted to develope the egg by the heat of his hot- 

 bed ; but he only raised monsters, a result which he attributed 

 to the unsteady application of heat.f It must, however, be 

 observed, that deviations from the correct temperature are inju- 

 rious and fatal only in proportion to the grade of vital energy 

 w^hich the ovular embryon possesses. Thus we learn, from the 

 experiments of Spallanzani,J that the eggs of insects are better 

 able to sustain the vicissitudes of temperature than those induced 

 with more exalted vitality. Thus it is that the eggs of cold- 

 blooded animals bear with impunity such an increase or decrease 

 of temperature as is sufficient to destroy the animals themselves ; 

 for Spallanzani found tadpoles and frogs perished at 110°, but 

 their eggs only at 133°. 



If we pursue this inquiry, and quitting the animal kingdom 

 descend into the scale of vegetable existence, where the energies 

 of vitahty are still more feeble and obscure, we shall find th© 

 same relative power of sustaining heat or cold between the plant 

 and the seed, as I have stated to exist between the animal and 

 its eo-g. 



With respect to the relative destructive influence of vicissi- 

 tude of temperature upon the egg of birds in different stages of 

 developement, it would appear, from the interesting experiments 

 of Reaumur, that it is more destructive in the eailier stages of 

 incubation, especially diminution of temperature, but that 

 increased heat is more injurious in the advanced states of deve- 

 lopement. 



After having related the agencies of heat and cold, I may 

 mention that hght has also been found by Michelotti,§ of Turin, 



* The inhabitants of the single village Berme, situated in the Delta, about 20 

 le^ues from Cairo, among whom this art is alone practised, give life by means of their 

 mcmuls to two-thirds of the eggs entrusted to their care, amounting in one season, which 

 continues but for six months, to the astonishing sum total of 95,000,000. Corneille le . 

 Bruyn, torn. ii. has collected the observations of many travellers on this subject. Father 

 Sichard also gives us an interesting account of the same art ; and Keaumur has pub- 

 lished a very complete work, illustrated with numerous engravings. 



-}• The ancients were acquainted with the possibility of hatching eggs artificially. 

 Pliny (lib. x . cap. 55) says, that eggs laid upon beds of straw in a warm place, and 

 after being regularly turned from time to time, would, at the proper period, disclose th« 

 included animal. Pliny moreover states, that lavia hatched a chicken by the warmth of 

 her bosom. Gesner and Aldrovandus have collected tlie passages of the ancients, and 

 those of the authors of their own time, that mention the method of hatching eggs by dung. 



4: Spallanzani. Tracti on the Nature of Animals and Vegetables. 



§ Journal de Physique, Ventote, An. ix. 



