922 RECORD OF CURRENT RESEARCHES RELATING TO 



might gradually travel inwards, remaining connected with the sense- 

 organ at the surface by protoplasmic filaments, which would then 

 constitute nerves. The rudimentary eye would at first merely consist 

 partly of cells sensitive to light, and partly of optical structures con- 

 stituting the lens, which would throw an image of external objects 

 upon it, and so convert the whole structure into a true organ of vision. 

 It has thus come about that, in the development of the individual, the 

 retina or sensitive part of the eye is first formed in connection with 

 the central nervous system, while the lenses of the eye are indepen- 

 dently evolved from the epidermis at a later period. 



Terminations of Nerves in the Epidermis.* — Professor Eanvier, 

 in a paper on this subject, mentions an improvement which he has 

 devised in the method of using chloride of gold for investigations on 

 the ultimate nerve-endings in tissues, the process of Loewit, though a 

 great improvement on that" of Cohnheim, having disadvantages. 



In the first place Professor Eanvier placed the tissues with the 

 nerve terminations two to four hours in a mixture of chloride of gold 

 and formic acid which had been boiled and then cooled. After 

 removal and washing, the reduction of the gold is effected either by 

 the action of daylight in slightly acidified water, or in the dark in a 

 solution of formic acid. By this method the terminations of the 

 nerves in muscles appear continuously arborescent instead of being 

 frequently interrupted as when Loewit's process is employed. At the 

 same time they contain some irregularities. For this reason Professor 

 Eanvier says it became necessary to invent a fresh process, and he 

 attempted to replace formic acid by one which would not have an 

 equally deleterious effect on delicate elements, and he believes he has 

 found it in lemon-juice. This, although altering nervous tissues by 

 its protracted action, yet preserves their form sufficiently long for it 

 not to be altered in the time requisite to procure the whole effect of 

 the chloride of gold. Preparations of the white or red muscles of the 

 rabbit treated successively with lemon-juice and chloride of gold, 

 preserve the nerve terminations not only continuously arborescent 

 but also remarkably regular. 



This process was adopted by Professor Eanvier in his investiga- 

 tion of the nerve terminations in the epidermis in general (employing 

 the snout of the pig, the nose of the mole, and the skin of the human 

 finger), and after a brief statement of the results, he says " the theory, 

 or rather the hypothesis, which I propose is founded on the facts 

 which I have just briefly expounded. The nerves which enter the 

 epidermis, whatever may be the form or extent of their ramifications, 

 are subject to a continuous evolution. They grow while at the same 

 time their terminations undergo a gradual degeneration ; this de- 

 generation leads to the formation of granules of nervous substance, 

 which become perfectly free and are soon transported into the inert 

 layers of the epidermis." 



Minute Structure of Smooth Muscular Fibres.t — The latest re- 

 searches of Professor Engelmann have led him to the conclusion that, 



* ' Quart. Journ. Micr. Sci.,' xx. (1880) pp. 45G-8, plate xxxvi. 

 + ' Rev. Inteniat. Sci.,' vi. (1880) p. 1«2. 



