466 SUMMARY OF CURRENT RESEARCHES RELATING TO 



in appearance, without sign of reticular or alveolar structure. Mito- 

 chondria are presentinall the cells of these growths as slightly refractive, 



large or small granules, rods and threads. They can be followed and 

 studied for hours in the living unstained cell. The mitochondria may 

 be scattered throughout the cytoplasm, or they may be located around 

 the nucleus or around the idiozome. Any one mitochondrium may 

 change its position in relation to another, or to the cell as a whole. 

 They may scatter or condense. During mitosis they become more 

 evenly scattered, except in the spindle area, where they^ are usually 

 absent. Their shape is very variable, and one may assume fifteen or 

 twenty shapes in ten minutes. They may divide or fuse ; they vary 

 greatly in size ; they appear to increase or decrease in size without fusion 

 or division. They vary in number from two or three to over two 

 hundred, and are not constant for any one kind of cell. 



Degenerating mitochondria become first a series of granules ; later 

 the granules become vesicles, and then separate into a number of small 

 finely granular rings which stain like the cytoplasm rather than like 

 mitochondria. They are more or less scattered in an indifferent manner 

 during mitosis, and about one-half the quantity goes to each daughter- 

 cell. 



Mitochondria are extremely plastic, but they are not specific. One 

 type changes into another. They are distinguishable from other 

 granules by their staining reactions. They are greatly increased in 

 number and quantity in giant cells. Mitochondria appear to arise in 

 the cytoplasm, and to be used up by cellular activity. They are, in all 

 probability, bodies connected with the metabolism of the cell. 



Mitochondria in Vertebrate Nerve-cells.* — E. Y. Cowdry has 

 studied the comparative distribution of mitochondria in spinal ganglion 

 cells in Vertebrates. They occur in the spinal ganglion cells of man, 

 monkey, guinea-pig, white rat, pigeon, snake, turtle, frog, and Necturus. 

 They are characterized by the coustancy of their structure, distribution, 

 relative amount and microchemical properties. There is a reciprocal 

 relation between the amount of mitochondria and lipoid granules in 

 these cells. The coagulability of the Nissl substance, on fixation, in- 

 creases progressively in the gradation w 7 hich exists between the small 

 and the large spinal ganglion cells of man, monkey, guinea-pig and 

 white rat. 



Histogenesis of Selachian Liver.f — Richard E. Scammon gives a 

 detailed account of the histogenesis of the Selachian liver. His material 

 was chiefly obtained from Squalus acanthias, but reference was made to 

 skate, torpedo, and other types for comparison. He describes the 

 development of the hepatic parenchyma, the minor bile ducts, the 

 hepatic mesenchyma, and the hepatic sinusoids. The adult liver is 

 divergent from the common Vertebrate type in the great accumulation 

 of fat in the hepatic cells, in the comparatively slight development of 



* Amer. Journ. Anat., xvii. (1915) pp. 1-28 (3 pis.), 

 f Amer. Journ. Anat., xvii. (1915) pp. 245-336 (7 pis.). 



