TRANSACTIONS OF SECTION I. tSlS- 



microscopically it consisted of masses of the epithelial scales of the crop mucosa 

 loaded with fat globules. An analysis made for Bernard by Leconte gave — 



' Casein ' and salts 23-23 



Fat 10-47 



Water 66-30 



No sugar was present — a fact noted also by Hunter. 



Hasse (1865) and more recently Max Teichmann (1889) have also written on 

 the subject from the histological point of view. 



The lateral pouches of the crop of the non-breeding pigeon are not glandular ; 

 the epithelium is stratified and free from fat, the submucosa provided with small 

 vascular papillje. 



The change in the crop membrane necessary for the formation of the ' milk ' 

 commences during the incubation of the eggs, and though not visible to the naked 

 eye till two or three days before hatching, makes itself evident by the appearance 

 of fat-droplets in the cells ten days before this event. The main change consists 

 in a great thickening of the epithelium, accompanied by rugose folding with reticu- 

 lation, while at the same time the structure becomes enormously vascular and 

 capillaries penetrate the epithelial layers (Hasse and Teichmann). 



Small pellets of curd-like matter form in the pits of the reticulated surface, and 

 as soon as the young are hatched these are transferred by the parents to the crops 

 of the ' squabs,' often to the extent of 40 percent, of the weight of the bodies of the 

 young. 



In its histological features the process of formation of the ' milk ' resembles more 

 closely that of the formation of sebum than of milk, for whole masses of fat-holding 

 cells are cast off from the walls of the pits in the membrane ; yet, unlike tho 

 sebaceous process, the nuclei of the cells persist. 



Interpapillary involutions, then, of the thickened stratified epithelium of the 

 crop act as sebaceous glands during the period of formation of the ' milk.' 



This period lasts for from seven to nine days after hatching, and the maximum 

 of activity is reached about the second day after hatching. 



The young are fed almost exclusively on this substance for the first three days, 

 though a few crushed grains are also supplied by the parents. The parents appear 

 to crush the grains at first, though later they are supplied whole. This fact is 

 accounted for by the condition of the gizzard membrane of the early ' squab,' for 

 the horny secretion of the tubular glands of the mucosa takes some days to con- 

 solidate. No digestive ferments are supplied by the parents along with the ' milk/ 

 and the proventriculus of the J'oung ' squab ' pigeon, even at twelve hours, is rich 

 in proteolytic ferment, its glycerine extract digesting fibrin with ease. The crops 

 of neither adult (breeding or non-breeding) nor young birds form any amylolytic 

 or proteolytic ferment; in both cases, however, multitudes of bacteria and cocci 

 are present, and the acidity of the contents (reaction of Uffelmann, but no reaction 

 with phloroglncin and vanillin) is probably due to lactic fermentation. The 

 pancreas of the * squab ' is capable of digesting starch at the time of hitching. 



In the ' squab ' the cell bodies of the 'milk' are dissolved oft" by the secretion 

 of the proventriculus, and the fat set free in the gut is found in the cells of the villi, 

 and also in the leucocytes of the blood. The faeces of the ' squab ' are fat-free, 

 though at an early stage they contain considerable proteid. 



Thougli sugar is undoubtedly absent from the ' milk,' a young ' squab ' pigeon 

 before it has received an)^ food contains sugar. In one case a triple alcoholic ex- 

 tract of a minced and finally pulverised ' squab ' yielded over -2 per cent, of its 

 body weight of reducing sugar, while a subsequent triple aqueous extract gave -16 

 per cent, of the body weight of an amylose yielding sugar on boiling with dilute 

 sulphuric acid. This amylose strucii no colour with iodine, and attempts to demon- 

 strate glycogen in the bodies of unfed ' squab ' pigeons have failed, though the 

 pectoral muscles of adult birds are very rich in this substance. 



As regards the proteids of the * milk,' extracts with ' normal saline solution ' 

 by trituration and digestion with thymol at 40° C. show absence of albumins, 

 proteoses, and peptones ; presence of globulin and of caseinogen (clot with rennet, 



