336 NORMAN CLTVE NICHOLSON 



Brains of mice were fixed by injection in the regular manner, 

 with the formaUn bichromate mixture to which in one case 0.5 

 per cent, in another 1 per cent, in a third 2.5 per cent, in a 

 fourth 5 per cent and finally 10 per cent of acetic acid had been 

 added. They were carried through and stained in the usual 

 way. 



No mitochondria were found after using the mixture contain- 

 ing 10 per cent acetic acid except in the cells of the hypophysis. 

 This was also true in the case of the 5 per cent mixture. With 

 increase in concentration of acetic acid the sections became more 

 and more difficult to stain and required longer and longer treat- 

 ment with permanganate and oxalic. The fluid containing 2.5 

 per cent acetic acid gave apparently the same fixation as the 5 

 per cent mixture, but the 1 per cent acetic mixture preserved the 

 mitochondria in the Purkinje cells of the cerebellum and de- 

 stroyed the mitochondria in the nerve cells of the medulla. 



With regard to variations in staining reactions it need only 

 be said that we do observe mitochondria taking the stain more 

 intensely in certain parts of the cell. This is often the case in 

 the region of the axon hillock. As the staining reaction does not 

 occur regularly and inasmuch as it may be due to differences in 

 the degree of mordanting with the bichromate I am not in- 

 clined to attach much significance to it. Moreover when mito- 

 chondria are very abundant they sometimes stain more intensely, 

 which may be due to the presence of the stain in greater mass and 

 consequently washing out more slowly than where only a few 

 mitochondria occur. Careful search has not revealed any definite 

 difference in the staining reactions of the different forms of 

 mitochondria, although one might expect this, if differences in 

 morphology were assumed to be related to differences in density. 



DISCUSSION 



Significance of morphological variations in mitochondria. The 

 true significance of the morphological variations in mitochondria 

 is unknown. Yet the demand for information is very insistent 

 as it is highly desirable that we should in some measure under- 

 stand the variations which unquestionably do occur both in 



