584 DES. GEORGE AND EEAKCES E. HOGGAN ON 



is evident tliat it will be of equal application over all tlie subepi- 

 dermic plexus of nerves, even w^bere no cells exist, and that tbis is 

 really tbe cause of tbe presence of non-meduUated nerve-fibrils 

 witbin tbe epidermis. Moreover a careful examination of suitable 

 specimens vpill sbow tbat, altbougb for some time sucb fibrils 

 continue to be spun out or drawn out into tbe epidermis, tbey are 

 continually rupturing at tbe base, and even during tbeir passage 

 tbrougb tbe epidermis. In tbe former case tbe epidermic cells 

 lose catcb of tbe dermic end of tbe fibril ; and subsequently no 

 intraepidermic fibril vnll appear to grow at tbat spot, wbile tbe 

 broken fragment gets rapidly carried to tbe surface and tbrown 

 oif witb tbe worn epidermic cells. Tbis continual entanglement 

 is equalized by tbe continual breaking at tbe dermic surface of 

 intraepidermic nerves ; and tbus it is tbat a very old animal 

 sbows no greater quantity tban a young animal of sucb fibrils, 

 perbaps even less, as we bave ourselves seen — a feature due 

 probably to a slower development of epidermic cells in tbe older 

 animal. But wbat we bave said of tbe entauglement of fibres in 

 tbe epidermis applies equally to tbe cells tbemselves, wbich 

 leads us on to another important problem hitherto unsolved, 

 altbougb often attempted, namely the origin of tbe cells of Lan- 

 gerhans. 



Origin of the Cells of LangerJians. 

 It would appear, from our preparations, tbat tbe cells upon tbe 

 course of tbe non-medullated nerves become quite as often entan- 

 gled in tbe epidermis as tbe intraepidermic fibrils, whether these 

 cells be solitary or belonging to large ganglionic groups. "We 

 bave already alluded to tbe fact tbat sucb cells often lie squeezed 

 between the lower layer of epidermic cells ; and were it not for 

 sucb appearances as are shown in fig. 19, Plate XV., we should 

 have been inclined to consider tbe position of tbe nerve- 

 cells among tbe lower cells of tbe epidermis tbe prime factor 

 leading to tbe presence of intraepidermic fibrils. There can be, 

 however, no doubt that this is also a constant cause of tbeir 

 presence there ; but at tbe same time we cannot admit tbat sucb 

 groups of cells lie normally performing tbeir functions wbile 

 imbedded two or three layers of cells deep in the epidermis. 

 Be that as it may, it is undoubted tbat sucb nerve-cells get car- 

 ried away into tbe epidermic stream. If tbe connecting fibrils 

 between tbe cells in a group are weak, the cells may be broken ofi", 



