igo THE JOURNAIv OF PHARMACOLOGY. 



The majority of hairs shows an entirely different construction at 

 various cross sections. A good illustration of this will be shown later on 

 by three cross sections of a cat's grannen and wool hair. 



Construction op Hairs and Wools in General. 



The greater majority of hairs are composed of three different kinds of 

 tissue. One or several layers of epidermal cells (epidermal scales) are 

 found on the outside, in the center is a strand of diversely constructed 

 elements mostly of a parenchymetic nature, known as medulla (pith, 

 marrow). Surrounding the medulla and between it and the epidermal 

 scales is a fibrous portion, the rind, the fibres being either thin walled or 

 thickened. 



Any one of these tissues may be lacking at intervals. If the epiderm is 

 absent it has been rubbed off ; this occurs frequently at the tips of the 

 grannen hairs of cats, etc. The fibrous layer or rind is often so slightly 

 developed that it is easily overlooked, especially when the medulla has be- 

 come unusually large. But in many instances it is missing even in the 

 broadest portion of some thick hairs of the deer. 



On the other hand, there is frequently no medulla in wool or grannen 

 hairs, and then again as regards bulk or volume it may constitute the 

 chief mass of the hair. 



Breadth and length of hairs vary greatly, not only when comparing 

 hairs of different animals, but also when comparing hairs from the same 

 animal. The finest wool hairs of sheep are scarcely lo p.. across, yet there 

 are some grannen hairs which measure more than lOo p-. Not only varia- 

 tions in measurements, but also the arrangement and construction of cer- 

 tain tissues, and especially the nature of the elements of the tissue furnish 

 many clues to determine the hair. 



The epidermal scales vary greatly as regards number of layers, usually 

 there is but one arrangement of the same, whether imbricated or lying side 

 by side, their color, shape, etc. (bristles are an exception). 



Their free outer edge may be quite thin ; in that case the hair is apt to 

 be quite smooth, and its contour is regular, even, and not serrate. But it 

 the outer edge and eventually the whole scale is thick then the microscope 

 will show a serrate appearance on both sides of the hair. These serrations 

 may be acute or blunt, decided or not, etc. Hairs used for felting are 

 characterized by these scaly grooves. 



The scales of the epiderm of the hair are either so large that even one 

 scale may surround the hair like a cuflF, or it may require two or more 

 to do this, as is the case in thick hairs. On thick hairs the scales are 

 often so close that the surface seems to be entirely covered with wavy 

 cross-lines which are caused by the contours of the edges and often pre- 

 sent a gnawed appearance. 



