72 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



VI. DISTRIBUTION. 

 DISTRIBUTION IN ORGANISMS. 



Mitochondria seem to be i:)resent in all organisms from man to the most lowly 

 protozoon and from the angiosperms to the fungi, but their existence is doubtful 

 in the myxomycetes, the schizomycetes, and most of the algie. 



Some think that the mitochondrial substance is here present in solution, and 

 this idea is supported by the staining reactions of certain bacteria. It occasionally 

 happens that tissues prepared for mitochondria have been invaded by bacteria, in 

 which case the bacteria stain just like the mitochondria by the Benda method, 

 with iron hematoxylin and with fuchsin methyl green. I have found that large 

 bacilli contain granules which stain intensely and apparently specifically with 

 janus green. They resemble in distribution the so-called polar granules. Smaller 

 forms often stain diffusely. 



Others consider the mitochondrial substance to be really absent. According 

 to them its function is carried on by the chloroplasts. The fact that mitochondria 

 diminish in number progressively with the development of chloroplasts in the 

 higher plants lends some support to this view. Mitochondria may even be entirely 

 absent when the full complement of chloroplasts is attained. 



We know of no other exceptions in the distribution of mitochondria, but it 

 must be borne in mind that comparatively few organisms have been investi- 

 gated as compared with the magnitude of the phylogenetic series and excep- 

 tions may be brought to light at any moment. 



DISTRIBUTION IN TISSUES. 



Mitochondria occur in all the tissues of both plants and animals, with few 

 exceptions, wherever protoplasm is active; except, of course, in the plants already 

 mentioned. They are found in epithelial tissues, muscular tissue, bone, and all 

 others, except in the terminal stages of cytomorphosis ; and this (according to N. H. 

 Cowdry) is one of the greatest points of similarity between these granulations in 

 the plant and animal kingdoms ; that is to say, their progressive diminution and 

 final absence in the later stages of the life of the cell. It will be discussed in detail 

 on page 78. 



DISTRIBUTION IN CELLS. 



Within individual cells mitochondria are, in the vast majority of cases, dis- 

 tributed indifferently, without definite order, throughout the cytoplasm; but there 

 are some notable exceptions, examples of which may be seen b.y reference to plate 1. 



The distribution of mitochondria with respect to polarity in secreting cells in 

 animals is most remarkable. In the acinus cells of the pancreas (plate 1, fig. 9) 

 the mitochondria are most numerous in the basal region next the basement mem- 

 brane. They are long and filamentous and are, in a general way, distributed parallel 

 to the long axis of the cell, streaming from the basement membrane toward the 

 lumen. A similar arrangement obtains in other glands like the vesicula seminaUs 



