THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 69 



Branching filaments are found in association with them and may constitute a 

 stage in their formation. The strands of the network are of the same girth as the 

 branching forms and of the individual filaments, except perhaps at the nodal points, 

 where they may be slightly enlarged. It is still impossible to say whether the net- 

 works arise through a fusion of many mitochondria or by outgrowth of separate 

 ones. They are difficult to preserve in fixed tissues by reason of the tendency of 

 fixatives to cause fragmentation. Where they are found in fixed preparations we 

 may be sure that they occurred in the living state. So far as we know at present, 

 they are not associated with any definite function on the part of the cell. 



Large spherical mitochondria are usually on the border-line between true 

 rnitochondria and lipoid droplets. They represent a stage in the transformation 

 and may be found in any tissue where the change is taking place. They may be 

 seen to the best advantage in the nervous system, in the cells of the spinal ganglia, 

 where all stages in the metamorphosis may be made out. When the mitochondria 

 assume a diameter of about 3 or 4 m they begin to become more and more resistant 

 to acetic acid and clump together in the familiar lipoid accumulations. The ques- 

 tion is rather complicated, however, because large spherical mitochondria, of much 

 the same appearance, may be produced by poor fixatives as well as by good fi.xatives 

 which have penetrated badly. We must know the tissue. This warning is par- 

 ticularly applicable to large spherical mitochondria with clear centers and to ring- 

 shaped forms, which should always be regarded with suspicion and interpreted 

 with caution. 



N. H. Cowdry (1917, p. 225) summarized his work on the morphology of 

 mitochondria as follows: 



"Their morphology is identical in plants and in animals; they assume no forms in the 

 one which are not present in the other; they undergo similar variations in size and shape in 

 different tissues and in different cells in both. If it were possible to view mitochondria 

 dissociated from their environment, it would be impossible to decide whether they came 

 from plant or animal tissues, provided they did not contain starch, pigment, or some other 

 easily recognizable substance, to serve as a clue." 



The little-known condition of chondriolysis is of interest. The mitochondria 

 lose their definite form, whatever it may be, and give rise to a diffuse deposit of 

 material staining with mitochondrial stains. It is of frequent occurrence in the 

 nervous system in normal conditions and is conspicuous in other organs in patho- 

 logical states (page 136). We should bear in mind the possibility that in all cells 

 individual mitochondria go into solution and gradually fade away and reappear 

 again, even though the change escapes our observation, except in special cases like 

 that of the nervous system. Something similar has been described in the supra- 

 renal by Mulon (1912, p. 36). 



Speaking in a general way, all mitochondria have smooth and even outlines, 

 no matter how bizarre their forms may be. Each merges into the other through 

 imperceptible transitions, so that any terminology is more or less arbitrary. No 

 difference can be detected in the solubilities or in the staining reactions of the 

 different forms. A fundamental distinction may, however, be made between 



