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XXVI. — Some Observations on Incubation. By John Davy, M.D., F.R.S., 



Lond. and Edin. 



(Read April 16, 1866.) 



The observations which I have now the honour to submit to the Society were 

 made chiefly with the intent to endeavour to ascertain whether, in the instance 

 of the egg of the common fowl, that which may be presumed to be vital action 

 can for a while be arrested, and yet be capable of renewal. Whilst this was the 

 main object kept in view in conducting the trials, a secondary one was to observe, 

 however cursorily, the changes which take place in the contents of the egg when 

 vital development has been prevented. 



Of the many experiments I have made, during a period of more than two years 

 that my attention has been directed to the inquiry, I shall select those, the results 

 of which were best defined, or were least ambiguous. Considering the obscurity of 

 the subject, it seems best to give the particulars of each of the selected trials, 

 though, in so doing, I have to fear that the details may prove tedious. 



In all the trials, newly or recently laid eggs were put under the hen for in- 

 cubation, with those which were the special subject of experiment. 



I. Of Unimpregnated Eggs. 



The trial with these was made as a preparatory measure in relation to those 

 which were to follow. 



Four eggs were selected, obtained from a hen that had been kept apart after 

 her last sitting. Of these, three in their fresh state were put under a hen with 

 eleven ordinary eggs ; the fourth was left exposed to the air in a room, the tem- 

 perature of which varied from about 60° to 65° Fahr. on the 15th June, the day 

 they were placed for incubation. 



No. I weighed 727'5 grs. l No. 3 weighed 801*6 grs. 

 2 ... 8515 „ 4 ... 8434 „ 



On the 9th of July the eleven impregnated eggs were hatched, producing healthy 

 chickens. The three unimpregnated were found to be little altered. Again 

 weighed, the loss of each, per cent., was as follows : — 



No. 1, . 



14-6 grs. 



No. 3, . 



.. 12-3 grs. 



2, . 



.. 13-7 „ 



4, . 



.. 2-7 „ 



The three from under the hen sank in water. Each broken under water, yielded 



VOL. XXIV. PART II. 4 Z 



