THE JOURNAL OF PHARMACOLOGY. 191 



On thin hairs the scales are loosely arranged, giving the hair the appear- 

 ance of being short limbed. Frequently the epidermal scales at the tip of . 

 the hair seem to be drawn up like a toothed (frayed) rag, especially notice- 

 able in the wool of the rodents, consequently causing them to appear un- 

 evenly striped, and also giving the hairs of the carnivora a dainty appear- 

 ance. 



The fibers of the rind are comparatively short, at the same time thin 

 walled to thick walled. Their length varies from 50 !j.. to several mm.; in 

 the case of a sheep they measure 80 il The fibers are usually flattened 

 and in such a manner that the radial diameter is the smaller one. There- 

 fore the wall halves lie very close and the lumen, when a cross section of 

 entire hair is made, is invisible or only seems like a fine tangential line. 

 It frequently happens that certain rind fibers are larger or show a broader 

 lumen. These represent what will further on be termed fiber spaces. 

 Longitudinally they seem like thicker isolated stripes. The longitudinal 

 striations of many hairs, especially those without a medulla, the pithless, 

 are caused only by the rind fibers and not as might be supposed from the 

 striations of the epidermal cells. In colored hairs the pigment is found, 

 only in the fibers and pith cells, generally in granules or masses with homo- 

 geneous contents, stored on the walls, not infrequently coloring even the 

 cell walls ; the latter instance occurs in dark bristles. 



The medullary or pith cells show all intermediary forms between long 

 fibers or narrow cylinders to thin plates (besides these there are other 

 deviations), but usually they are more or less roundly parenchymatic or 

 shortly cylindrical ; usually thin walled, but frequently the cross walls 

 which lie perpendicularly to the length of the hair seem to be quite thick. 

 This is due to the fact that the contents of the cell, which are usually 

 highly colored, have been stored on these walls. The cross walls of the 

 pith frequently tear (break) partially, and in this way a common medul- 

 lary channel is formed. But in the grannen hairs of some fur-bearing 

 animals the pith cells finally communicate. 



If a transverse section shows that the cells are arranged singly, then 

 there will be but one row, or there are several next to each other. The 

 latter occurs frequently in a very regular manner; shown in grannen hairs 

 of some rabbits. 



When the medulla" is composed of numerous rows of cells, those in the 

 interior will be larger and more thin-walled. The greater part of the 

 lumen of medullary cells is filled with air, especially in white and light 

 hairs. The hairs of some ruminants have a pith that at intervals is in 

 the form of single cells, in small groups or short longitudinal rows. 

 These are known as "pith plates," and are very characteristic. The 

 pith cells are always absent at the base and natural tip of a complete hair 

 as well as in the finer hairs of the ruminants ; but the wool of rodents, 

 (insectivora and carnivora) shows a symmetrical single row of pith cells. 



