394 MANUAL OF HISTOLOGY. 



frequently display an extensive folding back of the cells towards the bulb, giving rise 

 to the appearance of encircling fibres. 2. The medullary portion of the hair is the only 

 part about which there exists at present any considerable difference of opinion. The 

 presence in it of air was first pointed out by Griffith in the Loud. Med. Gazette, 1848, p. 

 844. On this point no doubt can be entertained. Steinlin held the medullary mass to 

 be a process of the papilla of the hair, consisting of cells, and extending into the shaft. 

 The lower part is, according to him, vascular, and made up of soft cells, while above, 

 the vessels become obliterated, and the cells shrink, making room for the accommo- 

 dation of air, so that the medulla might be said to be formed from the dried papilla. 

 Reichert supposes the dried remainder of the papilla to occupy the interior of the 

 medulla in the form of a delicate axial thread, and likens it to the "pith of a feather." 

 In some of the mammalia such an extension of the papilla into the shaft of the hair 

 does take place, and even far up into the latter, but in man it is doubtful that this 

 occurs. The representation given in the text is that most generally received, and 

 probably the simplest expression of observation. It is likely also that many com- 

 munications exist between the residual cells, which explain the rapid readmission of 

 air. 



216. 



The hairs, like cuticle and the nails, are numbered among the so-called. 

 horny tissue*, in that from them all, by treatment with alkalies, that mixture 

 of metamorphosed albuminous matters can be obtained, to which the name 

 of keratin (p. 21) has been given. The complex structure of the hair, 

 however, renders this analysis of less value than that of the two other 

 more simple tissues. 



Microchemical reaction shows that, in the hair and its envelopes, the 

 young recently-formed cells are still composed of ordinary albuminous 

 materials, so that even the more feeble attacks made by acetic acid and 

 dilute solution of the alkalies are capable of destroying their membranes, 

 and, soon after, the nuclei in the case of the latter reagents. This is the 

 case with the rete mucosum of the hair follicle, the external root-sheath, 

 and also the root of the hair. On the other hand, we are met by a most 

 striking insensibility to the action of chemicals in the cellular layers of 

 the internal root-sheath and cuticle of the hair, with the exception of 

 the most internal portion of both tissues bordering on the bulb. We 

 find that even concentrated sulphuric acid and alkaline solutions have no 

 action on the cells, even when the latter are treated for a considerable 

 time with these fluids. The latter do not even produce any amount of 

 swelling up in the elements, so that we have at all events peculiar kinds 

 of combination before us in these tissues. 



The action of sulphuric acid on those dry and horny cellular plates 

 which form the cortical portion of the hair, causes them to separate 

 readily from one another, while alkalies produce a swelling up of the 

 cortical mass, and solution of the whole when dilute and at an elevated 

 temperature. 



The cells likewise of the medullary mass can be recalled from the 

 shrunken condition in which we find them in the mature hair to their 

 original tense round form by these reagents. 



The transparent internal layer of the follicle, finally, manifests, as has 

 been already mentioned, all the insensibility of the elastic hyaline 

 membranes. 



The solubility of hair in solutions of soda and potash, with previous 

 swelling up, repeats, as we have already stated, what takes place with 

 epidermis and nail tissue under similar treatment. The products of the 

 combustion of hair also are similar to those of the latter. An analysis of 

 Van Laer's will serve as an example : 



