OBSERVATIONS ON INCUBATION. 349 



absolutely suspended. Even congelation itself, it may be conjectured, may be 

 compatible with the retention of a low vital force, more or less morbid or de- 

 ranged ; at least, congelation, I have found, does not entirely arrest action in the 

 blood, ammonia being formed in it, and evolved from it when frozen.* 



Relative to the varied changes witnessed in the aborted or unproductive eggs 

 — some amounting to putrefactive decomposition, some indicative of the forma- 

 tion of new compounds, some so inconsiderable as to be only just appreciable — it 

 is difficult to offer any satisfactory explanation, especially as, in every instance of 

 incubation, all have been apparently very similarly acted on. Mr Hunter has 

 expressed the opinion that eggs which have " not hatched become putrid in 

 nearly the same time with any other dead animal matter, f This statement is 

 not supported by the preceding results. At one time I was disposed to infer, 

 from various experiments I had made, some of which are to be found in the last 

 volume of my " Physiological Researches," that the circumstance which most 

 favours the putrefactive change in the egg is the commingling of the white and yolk. 

 But from later experiments, especially one recently made, my confidence in this 

 opinion has been shaken. The experiment was the following : — Eight newly laid 

 eggs were wrapped in paper, placed in a basket, and covered with paper, in a 

 room, the temperature of which ranged from about 50° at night to 55° by day. 

 The placing them was begun on the 27th of November, and continued as follows, 

 each egg being weighed at the time : — 



No. 1, November 27, weighed 831 3 grs. 



2, ... 28, ... 9910 „ 



3, ... 30, ... 8425 „ 



4, December 2, ... 8934 „ 



No. 5, December 5, weighed 890 - 5 grs. 



6, ... 8, ... 862-4 „ 



7, ... 10, ... 8690 „ 



8, ... 13, ... 1012-5 „ 



They were left undisturbed until the 30th of January, when they were taken out 

 and again weighed. 



No. 1 was found to have lost 2 - 4 per cent. 



2 3-2 „ 



3 ... ... 3-5 



4 3-3 „ 



No. 5 was found to have lost 29 per cent. 



6 30 „ 



7 30 



8 2-2 „ 



These eggs were now put- under a hen with five fresh ones. On the 28th of 

 February the latter were all hatched ; the former were found to have failed. 



No. 1 had sustained a further loss of 1 58 per cent. 



2 144 „ 



3 138 „ 



4 ... ... 16-6 „ 



No. 5 had sustained a further loss of 147 per cent 



6 122 „ 



7 121 „ 



8 ... ... 58 .. 



This trial was made on the idea that, by checking evaporation, and by perfect 



* See Transactions Roy. Soc. of Edin. vol. xxiv. p. 26. 

 f Philosph. Trans, for 1778, p. 29. 



VOL. XXIV. PART II. 5 B 



