488 E- V. Cowdry, 



tliey are thickly distributed in tlie axone hillock. Similarly in cells 

 stained by the acid fnchsin-toluidin blue method the same differences 

 could be more clearly made out. 



The iron hematoxj^in method of Heidenhain was applied to 

 material fixed in chrome-sublimate and the preparations obtained were 

 counterstained by Held's erythrosin-methylene blue method. The g'ran- 

 ules were thus tinged with red and could be distinguished from the 

 Nissl substance in blue and the mitochondria in black (fig. 10). 



It is therefore evident that this type of neurosome is quite 

 distinct from either the mitochondria or the Nissl substance. The 

 question, however, as to whether they are or are not artefacts cannot 

 be definitely settled until they have been demonstrated specifically by 

 vital stains. At present care must be taken not to confuse them with 

 mitochondria, and the following criteria for differentiation may be of 

 value: 



1. They are of irregular size and form, whereas the mitochondria 

 are minute, sharpl}^ delineated, rods of fairly uniform size. 



2. They are accumulated in the axone hillock; but the mitochondria 

 are distributed more or less equally throughout tlie cytoplasm. 



3. In general they are more numerous. 



4. They are seldom, if ever, seen after fixation in fiuids contain- 

 ing osmic acid, which as already recorded, are by far the most 

 suitable for mitochondria. On the other hand, they may be stained 

 to best advantage after fixations like Carnoy's 6:3:1 fluid, picro- 

 sulphuric acid, chromic acid, etc., which destroy mitochondria. 



The evidence for the identity of the second type of neurosomes, 

 that is to say, those which Held observed in his Altmann and iron 

 hematoxylin preparations, and the mitochondria is as follows: 



1. They are both very minute, clear-cut, straight or slightly 

 curved rod-shaped bodies, about three times as long as they are broad, 

 distributed equally throughout the cytoplasm, not aggregated in the 

 region of the axone hillock, where tliej are oriented parallel to the 

 neurofibrils. Furthermore, a comparison of figures 2 and 5, which 

 are of iron hematoxylin and Altmann preparations, with figures 1, 3. 

 4, 6 and 7, representing mitochondria by various methods, shows that 



