568 SUMMARY OF CURRENT RESEARCHES RELATING TO 



medullated fibril accompanies the stout medullated fibre, and on its 

 approach to the inner cylinder, divides dichotomously to form the net- 

 work, which the preparations showed clearly picked out in blue. 



Nerve-endings in Frog.* — Prof. Julius Arnold describes a very 

 simple method for demonstrating the nerve-endings in the tongue of the 

 frog. The tongue of a curarised frog is fixed on a Thoma object- 

 carrier, dusted with fine particles of methylen-blue, and covered with a 

 drop of 1 per cent, sodium chloride and a cover-slip. After 15-20 

 minutes the cells of the so-called nerve-papillae exhibit a bluish-green 

 tint, the colouring being confined to the surface and to the central 

 cells. Subsequently coloured cells appear at the periphery of the papillae. 

 Soon numerous intensely coloured granules appear beneath the epithe- 

 lium, which are later seen to be in connection with fine varicose fibrils 

 forming a dense sub-epithelial network. In the centre of the papillae 

 elements of various shapes appear, furnished with nuclei which are no 

 longer seen when the colouring becomes intense. The elements give 

 off forked or branched prolongations which sometimes cross the epithelial 

 cells, and pass between them towards the surface. 



Structure of Spleen.j — H. Hoyer has investigated the structure of 

 the capillary veins of the spleen, with a special view of determining the 

 nature of the circular fibres, described by v. Ebner as elastic tissue. 

 Careful observation at different periods of growth has convinced him 

 that the venous capillaries originally form a system of branched 

 endothelial tubes, imbedded in the framework of the spleen, and sup- 

 ported by the cells of the splenic reticulum. As the vessels become 

 increasingly functional with the growth of the organ, the reticular cells 

 surrounding them become modified and form a close investment around 

 them. Later these cells and their prolongations form a definite fibrillar 

 sheath about the capillaries, and the fibrils give under certain conditions 

 the reactions of elastic tissue. The author believes that the reason why 

 this reaction is so difficult to obtain, is that the elastic tissue is present 

 only in very small amount within the connective-tissue sheath. The 

 result is to give the walls of the venous capillaries great firmness, and 

 so adapt the spleen for what the author regards as its main function, 

 that of a blood-filter. 



Structure of Epidermis. J — Dr. Franz Weidenreich has studied 

 the structure and process of cornification of the epidermis of man, and 

 finds that the cells of the horny layer are more or less strongly flattened 

 non-nucleated structures. Each consists of a cornified membrane, a 

 network of fine threads consisting of modified protoplasm, and an 

 empty nuclear space. The meshes of the network are filled in the super- 

 ficial cells with pareleidin, in the deeper with eleidin, otherwise the 

 structure of the cells is identical from the stratum granulosum to the 

 surface. The horny membrane arises from the modification of the 

 fibrillar exoplasm of the cells of the Malpighian stratum, the fibrilhvf 

 network originates from the persistent protoplasmic fibrils. The elei- 

 din originates from the keratohyalin, and its conversion into pareleidin 

 depends upon impregnation with sweat. There is no very striking. 



* Anat. Anzeig., xvii. Q900) pp. 517-9. f Tom. cit., pp. 490-7 (2 figs.). 

 X Arch. Mikr. Anat., lvi. (1900) pp. 169-229 (2 pis.). 



