MITOCHONDRIA IN PLANT AND ANIMAL CELLS. 2O3 



Osmic acid is the best preservative of mitochondria and the 

 worst penetrator and is therefore useless in the cells of the pea 

 radicle on account of their impermeable cellulose walls; yet it is 

 this quality of being an excellent preservative which makes it so 

 valuable in association with other chemicals. It does not cause 

 any artificial coagulation of the ground substance. 



Corrosive sublimate in saturated aqueous solution also pene- 

 trates the pea radicle very poorly; the pancrease not so badly. 

 However it preserves the mitochondria in the pea far better 

 than in the pancreas in spite of the fact that they are, in both 

 cases, somewhat shrunken. In alcoholic solution it is destruc- 

 tive, but it is difficult to tell whether this is due to the alcohol 

 or to the increased amount of sublimate. In Zenker's fluid the 

 injurious action of the sublimate is counter-balanced by the 

 presence of potassium bichromate. 



The action of acetic acid is so important that I have made a 

 detailed study of it as set forth in Table II. 



In the first place I have varied the concentration of acetic 

 acid in Regaud's mixture IV. B from o per cent, to 10 per cent. 

 With no acetic acid the mitochondria are normal; while with a 

 concentration of 2.5 per cent., or more, they are destroyed in 

 both tissues, showing that their degree of solubility is the same. 



I have also experimented with Zenker's fluid and I find that, 

 w T ith it, the mitochondria are on the whole much more resistant 

 to acetic acid. This may be due to the fact that the Zenker's 

 fluid was only applied for one day, instead of for five days like 

 the Regaud's fluid; or the presence of sublimate in the Zenker's 

 fluid may have tended to counteract the action of the acetic acid. 

 The mitochondria are fairly well preserved when no acetic acid 

 has been added to the Zenker's fluid. With increase in acetic 

 acid, up to 10 per cent., they become destroyed in the deeper 

 parts of the tissue, especially in the pea; while they are fairly 

 well preserved in the most superficial cells in both. In the pea, 

 also, the mitochondria are far more prone to become fragmented. 

 This difference between surface and interior seems to be a 

 question of penetration rather than of a difference in the mito- 

 chondria themselves. There is a simultaneous action of all the 

 ingredients of the fixative on the cells at the surface and here the 



