14 E. V. COWDRY 



this is due to the difficulty of keeping the nerve cell under obser- 

 vation, in approximately normal environment, for a sufficient 

 length of time. 



The lipoid globules are of about the same size in the different 

 animals. They are always spherical and vary from 1 to 5n in 

 diameter (measurements made on unstained cells in approxi- 

 mately isotonic media). Their arrangement in the cell is per- 

 fectly typical. They occur in clumps in any part of the cyto- 

 plasm. They sometimes extend into the processes, but rarely 

 attain a size of more than Ifj, when thus situated. They vary 

 in amount in different cells of the same animal, sometimes being 

 absent and sometimes present in abundance. The large and the 

 small cells show them in equal number. Their presence is not 

 accompanied by any sign of pathological change. 



The Nissl suhstaiice, also, occurs in the spmal ganglion cells 

 of man, monkey, guinea-pig, white rat, pigeon, snake, turtle, 

 frog and necturus. Its morphology is more variable than that 

 of either the mitochondria or the lipoid. It presents constant 

 differences in the large and in the small cells (30^* or less, meas- 

 ured in fixed tissues) of man, monkey, guinea-pig and white 

 rat. I am not yet prepared to make definite statements about 

 the other animals. In the cells, which have been fixed, it occurs 

 in irregular aggregates of variable size and shape, which are 

 absent in the axone hillock and are larger about the periphery 

 than in the more central parts of the cell; but in small cells it 

 is generally (though not invariabljO present as a diffuse, con- 

 tinuous, amorphous deposit. All gradations exist between these 

 extremes. Figure 10 shows some cells occurring in a single 

 section of a guinea pig's spinal ganglion prepared by Bensley's 

 method. At the top the diffuse condition is seen, at the bottom, 

 well formed Nissl bodies. It is not due to the distance of the 

 cells from the surface, and resultant variations in the rate of 

 penetration of the fixative, because the cell shown in figure 12 

 is in actual contact with the one illustrated in figure 10 d. They 

 both typify the condition mentioned although the fixative acted 

 on them both in the same way and at the same time. Fixation 

 in 2 per cent osmic acid and in Altmann's osmic bichromate 



