2OO N. H. COWDRY. 



hematoxylin, with fuchsin methyl green, with Altmann's fuchsin 

 picric acid and sometimes by the Benda method. The chief 

 results are briefly set forth in the following table, but a large 

 number of additional controls were made. 



In a general way, running our eyes down the table, we see 

 that the response of mitochondria to fixatives is the same in 

 plants as in animals. Similar fixations preserve them, modify 

 them and destroy them in much the same way in both. It also 

 shows that the technique is easy, not difficult, and that a number 

 of chemicals, which are generally thought to be destructive, will 

 fix them more or less satisfactorily. 



The standard mitochondrial fixatives, like Regaud ('10, p. 296) 

 II., III., IV. A and IV. B, Benda's modification of Flemming's 

 fluid, the acetic acid osmic bichromate mixture of Bensley, and 

 Zenker, without acetic, will fix them in both tissues. I have 

 found, however, that Regaud 's mixtures are by far the most 

 satisfactory because they do not produce the artificial coagula- 

 tion of the ground substance caused by the others. They also 

 preserve the true form of the mitochondria more faithfully; 

 though I have reason to suspect that in some cases, in plant cells, 

 they cause fragmentation and shrinkage. I have studied the 

 behavior of the ingredients of these fluids. 



Formalin is perhaps the most important since it penetrates 

 rapidly, retains the homogeneous appearance of the ground 

 substance and preserves the mitochondria satisfactorily. For- 

 malin alone (Sapehin, '15, p. 321) serves as an excellent fixative 

 for mitochondria. My best results w r ere obtained with a solution 

 of formalin of from 5 to 10 per cent, made up from ordinary 

 commercial formalin peutralized with magnesium carbonate. 

 More dilute solutions tend to cause a swelling of the mitochondria 

 and more concentrated ones a shrinkage; but different tissues 

 require different concentrations. Regaud advises a subsequent 

 mordanting with bichromate, but I find that this is quite un- 

 necessary. Used in combination with 3 per cent, potassium 

 bichromate, according to the directions of Regaud, formalin 

 gives the best of fixations with both the pea and the pancreas, 

 though in my experience the results may be even improved by 

 diluting the mixture with an equal volume of water as advised 



