32 SUMMARY OF CL'IflJENT IJKSEAltCIIES KELATING TO 



Structure of Epithelial Cells of Stomach and Intestine.*— Julius 

 Arnold describes in several types — frog and mammal — the varied 

 arrangement of granala-tlireads in the epithelial cells, and brings for- 

 ward evidence of their functional importance in metabohsm. "They 

 constitute an essential structural part of the cell ; they function in 

 absorption, assimilation, synthesis, and storage. Tliey also exhil)it 

 changes in the process of secretion. 



Paneth's Cells.t— Harry Kull finds that Paneth's cells arise by the 

 gradual transformation of goljlet-cells. Intermediate forms may be seen 

 in Lieberkiihn's glands in a starving mouse and in the fcetus, and also 

 in the villi. It seems likely that the cells whicli are formed in the 

 lateral parts of Lieberkiihn's glands get displaced upwards into the villi 

 or downwards into the fundus of the srlands. 



Heart-muscle of Humming-bird.:}:—}!. E. Jordan points out that 

 notwithstanding much careful microscopic work on mammalian cardiac 

 muscle, it remains an open question whether in the adult condition it is 

 syncytial or cellular. The opposing views are urged with equal cogency 

 by such authorities as, for example, Heidenhain and Zimmermann. 

 The designation of cardiac mnscle as a tissue or a syncytium depends 

 upon the interpretation given to the so-called intercalated disks or 

 junction lines (liauds of Eberth), whether or not they mark cell 

 boundaries. Jordan has studied this question in the heart of the 

 humming-l)ird, which was chosen because of its high organization. 



It may be noted, first of all, that intercalated disks rarely occur 

 below the level of birds (Jordan records a few in turtle, frog, and trout) ; 

 they do not occur in man and other mammals (e.g. sheep) until after 

 birth ; in the earlier stages of development in birds and mammals the 

 musculature is distinctly syncytial : the disks are apparently more 

 numerous in mammals than in birds, and they are not equally numerous 

 throughout all parts of the same heart. In short, they seem to indicate 

 increased differentiation of the muscle. 



Jordan's conclusion is that the cardiac muscle of the humming-bird 

 is truly syncytial. The intercalated disks cannot be interpreted as cell 

 boundaries or cement lines. They are structurally and tinctorially like 

 anisotropic bands, are closely related to them in position, and most 

 probably represent a definite functional state, or, perhaps, the effect of 

 function. 



Origin and Structure of Red Blood-corpuscles in Birds.§~-W. 

 Venzlaff describes the vascular supply of the medulla of the femur and 

 tibia of pigeons. Lymph-cells of various sizes are liberated from lymph- 

 nodi^es into the veins and become erythrocytes. .The plasma becomes 

 hyahne, a cortex is differentiated, the chromatin of the nucleus becomes 

 reticular, the nucleolus disappears, the hemoglobin appears. The ery- 

 throcytes break down in the blood after degeneration and disappearance 



♦ Arch. Mikr. Anat., Ixxvii. (1911) pp. 34G-7C (1 pL). 



t Aich. Mikr. Anat., Ixxvii. (1911) pp. 541-5G (1 pi. and 5 figs). 



X Amer. Record, v. (1911) pp. 517-27 (15 figs.). 



§ Arch. Mikr. Anat., Ixxvii. (1911) pp 377-4.^2 (1 pi.). 



