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SCIENCE 



[N. S. Vol. XXXIX. No. 1000 



other observers are to be found. In such 

 specimens, granules, rods, threads, loops and 

 networks can be arranged in a continuous 

 series ; in other words, there are to be found in 

 single stained preparations all gradations of 

 size and shape from the small and large 

 granules to short rods and long rods, to 

 threads of varying length, to anastomosing 

 threads and networks, which extend through- 

 out the cytoplasm and to rings and loops of 

 various shapes. 



Certain kinds of cells do, however, contain 

 characteristically shaped mitochondria. In- 

 testinal or stomach endoderm shows only 

 granules and short rods. Heart and smooth 

 muscle cells contain in addition to the usual 

 types large round and spindle-shaped mitochon- 

 dria. In the heart muscle cell the appearance 

 of the central body, probably the centrosome, at 

 the base of the nucleus, is much more definite 

 than in most cells. The mitochondria radiate 

 out from this central body as though under 

 the influence of the activity of the centrosome, 

 as is believed by Vejdovsky. 



By far the most important and interesting 

 are the observations on the living cells. In the 

 living cells the mitochondria are seen as 

 slightly refractive opaque bodies. They cau 

 be studied from minute to minute over a 

 period of several days if nec-essary. The mito- 

 chondria are almost never at rest, but are con- 

 tinually changing their position and also their 

 shape. The changes in shape are truly re- 

 markable not only in the great variety of 

 forms, but also in the rapidity with which they 

 change from one form to another. A single 

 mitochondrium may bend back and forth with 

 a somewhat undulatory movement or thicken 

 at one end and thin out at the other with an 

 appearance almost like that of pulsation, re- 

 peating, this process many times. Again, a 

 single mitochondrium sometimes twists and 

 turns rapidly as though attached at one end, 

 like the lashing of a flagellum, then suddenly 

 moves off to another position in the cytoplasm 

 as though some tension had been released. 

 Corresponding to the forms observed in the 

 stained preparations we find in the living 

 that granules can be seen to fuse together 



into rods or chains, and these to elongate into 

 threads, which in turn anastomose with each 

 other and may unite into a complicated net- 

 work, which in turn may again break down 

 into threads, rods, loops and rings. 



The mitochondria in a cell of a living 

 preparation of a piece of heart of a five-day 

 chick embryo studied on the third day after 

 the culture was made presented a very re- 

 markable picture. Eadiating out from the 

 central body at the base of the nucleus were 

 numerous granules, rods and thread-like 

 mitochondria. They were seen to elongate to 

 many times their original length, spreading 

 out through the cytoplasm and to anastomose 

 into a complicated network. About fifteen 

 minutes later this network broke up and con- 

 tracted into threads, rings, loops and rods and 

 granules. This entire process took place with- 

 out any noticeable change in the position or 

 size of the cell. 



The presence of fat is shown by the 

 Nilblew vital stain within the varicose mito- 

 chondria. We have not observed any con- 

 nection between the disappearance of mito- 

 chondria and the formation of fat within the 

 cell as stated by Dubreuil. 



The question as to whether the mitochon- 

 dria divide, so that one half of each mito- 

 chondrium passes into each daughter cell at 

 mitosis (Benda), is one of the most interesting 

 in the whole field of work upon mitochondria. 

 As yet we are unable to state definitely that 

 such a division takes place. In the cells of 

 the tissue cultures the behavior of the mito- 

 chondria is difficult to follow during mitosis, 

 since the body of the cell contracts to much 

 less than the normal size and its processes be- 

 come exceedingly long and delicate. All of 

 the mitochondria are drawn into the body of 

 the cell and become very short dumb-bell-shai)ed 

 granules during the late metaphase and ana- 

 phase. Owing to the very flat shape of the 

 cells (growing along the coverslip) the spindle 

 always appears horizontal to the coverslip and 

 the plane of cleavage perpendicular to the sur- 

 face. In some cells during the anaphase the 

 mitochondria were observed to collect in a 

 zone through which the cleavage plane will 



