1864.] 



of the Papilla of the Frog's Tongue. 



385 



to the defective method of preparation he employed, has failed to observe 

 points which had been seen by others who had written before him, and 

 which may now be most positively demonstrated. Hartmann's process 

 consisted in soaking the tissue for three days in solution of bichromate of 

 potash, and afterwards adding solution of caustic soda. It can be shown 

 by experiment that many structures which can be most clearly demon- 

 strated by other modes of investigation, are rendered quite invisible by this 

 process. Hartmann's observations, like those of the author, have been 

 made upon the papillae of the tongue of the little green tree-frog (Hi/la 

 arhored). 



With reference to the termination of the nerves in the fungiform papillse 

 of the tongue of the Hyla, the author describes a plexus of very fine nerve- 

 fibres, with nuclei, which has not been demonstrated before. " Fibres re- 

 sulting from the division of the dark-bordered fibres in the axis of the 

 papilla can be traced directly into this plexus. From its upper part fine 

 fibres, which interlace with one another in the most intricate manner, 

 forming a layer which appears perfectly granular, except under a power 

 of 1000 or higher, may be traced into the hemispheroidal mass of epithe- 

 lium-like cells which surmounts the summit of the papilla. This hemi- 

 spheroidal mass belongs not to epithelial, but to the nervous tissues. It 

 adheres to the papilla after every epithelial cell has been removed ; the 

 so-called cells of which the entire mass consists cannot be separated from 

 one another like epithelial cells ; fibres exactly resembling nerve-fibres 

 can often be seen between them ; and very fine nerve-fibres may be traced 

 into the mass from the bundle of nerves in the papilla. 



The fine nerve-fibres which are distributed to the simple papillae of the 

 tongue, around the capillary vessels, and to the muscular fibres of these 

 fungiform papillae, come off from the very same trunk as that from which 

 the bundle of purely sensitive fibres which terminate in the papillae are 

 derived. The fine nucleated nerve-fibres of the capillaries which the author 

 has demonstrated have been traced into undoubted nerve- trunks in many 

 instances, so that it is quite certain that many of the nuclei which have 

 been considered to belong to the connective tissue (connective-tissue cor- 

 puscles) are really the nuclei of fine nerve-fibres not to be demonstrated 

 by the processes of investigation usually followed*. These nerve-fibres in 

 the connective tissue around the capillaries are considered by the author to 

 be the afferent fibres of the nerve-centres of which the efferent branches 

 are those distributed to the muscular coat of the small arteries. 



The author's observations upon the tissues of the frog convince him that 

 the nervous tissue is distinct in every part of the body from other special 

 tissues. For example, he holds that nerve-fibres never pass by continuity 

 of tissue into the ' nuclei' (germinal matter) of muscular fibres, or into those 



* See " On the Structure and Formation of the so-called Apolar, Unipolar, and Bi- 

 polar Nerve-cells of the Frog," Phil. Trans. 1863, plate 40. fig. 44, 



