130 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



according to which the mitochondria play the part of plasts, choosing out and 

 selecting materials from the blood-stream and the cytoplasm, condensing them 

 and changing them, in their substance, into infinitely diverse products. Chemical 

 substances are thus supposed to be drawn in from the outside, not to be formed 

 through a transformation of mitochondrial material. Regaud thus resolves the 

 problem largely into one of permeability. His conception is, as he himself points 

 out, essentially a modification of the celebrated lipoid membrane theory of Over- 

 ton, the chief difference being that, according to Regaud, the lipoid substance 

 is said to be distributed throughout the whole cytoplasmic area in the form of 

 mitochondria instead of being confined to a layer on the surface of the cell. 



Specific cases of the alleged development of secretion granulations from mito- 

 chondria have been discussed under the heading of "Histogenesis" (p. 116). 



CONTRACTION. 



The view that mitochondria are directly concerned with the motor activities 

 of cells is of historic interest only. Benda (1903, p. 127) advanced it upon the 

 basis of the following considerations: (1) similarity in the microchemical reac- 

 tions of the dark bands of striated muscle and mitochondria; (2) the grouping of 

 mitochondria about the axial filament of the developing spermatozoon; (3) the 

 heaping-up of irdtochondria about the roots of ciUa in ciliated cells. Benda later 

 (1914, p. 25) modified his conception by making the statement that mitochondria 

 are concerned with the development of the motor organs of the cell, like myofibrils. 



Holmgren's (1909, p. 307) observations on changes in mitochondria in mus- 

 cular fatigue are of special interest here. He made ingenious experiments with 

 dragon-flies, holding them by the thorax between finger and thumb and allowing 

 them to continue beating their wings furiously for different lengths of time. He 

 found that granules which stained in a typical way with the Benda method and 

 with iron hematoxylin underwent definite alterations, depending upon the severity 

 of the fatigue. The granules changed their position, diminished in number, and 

 stained less intensely. These findings are certainly suggestive, to say the least, 

 but they have never been confirmed. They evidently merit further attention. 



Faure-Fremiet (in discussing the paper by Regaud and Mawas, 19096, p. 235) 

 records the observation that the mitochondria, gathered about the contractile 

 filament in the peduncle of vorticella, are unchanged at the moment of contraction. 

 Regaud (19086, p. 209) observed that the mitochondria in the ciliated cells of the 

 urinary tubules of cold-blooded vertebrates are few in number, are distributed 

 without apparent order, and have no relation to the cilia. Finally, Shipley (1916, 

 p. 444) discovered that there is no relation between the motility of Trypanosoma 

 lewisi and the amount of mitochondrial substance within them. 



IRRITABILITY AND CONDUCTION. 



Curiously enough, the jiroblem of mitochondria in this connection has so far 

 been untouched. This may perhaps be due to the reluctance of investigators to 

 even admit their existence in nerve-cells (see p. 101). Accordingly, it is a very 

 pertinent question to inquire whether there are alterations in the mitochondria in 



