CoxcERMxG Pigko.n's IMilk. 



lo: 



IS 



Jumping hfty years, and coming- to the year LS.-,(), 

 Llaude Bernard gives to the world the results attending 

 his investigations into this most curious problem of 

 Nature. Bernard found that this substance known a 

 Pigeons' milk consists of masses of the cells linino- th 

 crop, but that these cells differ from the normal Inas- 

 much as they are loaded with g-lobules of fat. In 

 Bernard's opinion the substance is more analogous to 

 sebum or the oily substance formed in the bird's tail- 

 gland, and with which it preens its feathers, than it is to 

 the milk of the mammal race of animals. This is in 

 full accordance with the earlier investigations of 

 Hunter, who agrees entirely with Bernard that the 

 substance forming the soft food of Pigeons is entireK- 

 free from sugar. 



THE CH.\XGES IN TH^; CROP. 



The changes occurring in the crop membrane dur- 

 ing the formation of the soft food, or when, as it ^^'as 

 quaintly put by Hunter, " the Pigeon gets in milk," 

 are as follows : — 



" The crop of the non-breeding Pigeon is simplj- 

 lined with layers of fiat non-fatt}' cells, the total thick- 

 ness of the cell-layer 'oeing apparently about the two 

 hundred and fiftieth part of an inch. These non-fatty 

 cells are placed over small vascular papill.K. During 

 the period of incubation these papilke grow, capillaries 

 from their vessels penetrate the superposed la>'ers of 

 cells, which increase most rapidly in number, and 

 manufacture fat. The thickness of the cell-layers is 

 now about one-sixteenth of an inch, and the surface 

 of the crop membrane becomes reticulated and pitted. 

 From now onward the fatty cell-layer becomes richly 

 supplied with blood, continues to grow at a great rate, 

 and as new cells are formed in its deep strata, so whole 

 masses are cast off at the surface, and this process occur- 

 ring especially in the pits leads to the formation of the 

 pellets of the soft food, or milk, found in the crop. 



THE STIMUIvATING AGENT. 



" As in the mammal, a fretus in utero is the stim- 

 ulus to action for the mammary, or milk, .gland, so 

 here the incubation is the stimulating agent, and this 



