( 234 ) 

 PROGEESS OF MICEOSCOPICAL SCIENCE. 



Difficulty of Experiments on Spontaneous Generation. — Mr. Crace- 

 Calvert, F.R.S., cites the following experiment in his first paper " On 

 Protoplasmic Life," read before the Royal Society (received May 8) : — 

 Although he was prepared, by the perusal of the papers of many 

 workers in this field, to experience difficulties in in-osecutuig the study, 

 he confesses he did not calculate on encountering so many as he met, 

 and especially those arising from the rapid development of germ-life, and 

 of which he had hitherto seen no notice in any papers which had come 

 under his observation. Thus, if the white of a new-laid egg be mixed 

 with water (free from life), and exposed to the atmosphere for only 

 fifteen minutes, in the months of August or September, it will show 

 life in abundance. From this cause he was misled in many of his 

 earlier experiments, not having been sufficiently careful to avoid even 

 momentary exposm-e of the fluids to the atmosphere. To the want of 

 the knowledge of this fact may be traced the erroneous conclusions 

 arrived at by several gentlemen who had devoted their attention to the 

 subject of spontaneous generation. 



Regeneration of the Corneal Epithelium. — Dr. Hjalmar Heiberg, of 

 Copenhagen, has written a very valuable paper on the above subject 

 which is reproduced in the ' Lancet.' A paper recently appeared 

 in Virchow's ' Archiv,' by Jvilius Arnold, on the same subject, who 

 came to the conclusion that the new cells which replaced the old, when 

 these had been detached, were derived from a finely granular blastema 

 that changes into protoplasm, and that in this protoplasm the new cells 

 arise by a process of free cell-formation. The correctness of this con- 

 clusion is contested by Dr. Heiberg, who maintains the view that 

 young cells are developed from the old, in which certain changes have 

 taken place. His mode of i)rocedure was to scratch the surface of the 

 cornea with a cataract needle in animals (frogs, birds, rats), and, after 

 the lapse of from eighteen to forty hours, to remove the eye andi examine 

 the cornea both by means of fresh sections and after careful prepara- 

 tion in solutions of chloride of gold (maceration for from three to five 

 minutes in a one-half per cent, solution of the salt). In certain prelimi- 

 nary experiments it was found that the injured part immediately after 

 the injury presented sharply-defined iiTcgular borders ; after six hours 

 tlie margins were considerably fiattened, so that the boundary of the 

 abrasion was much less distinct. After eighteen hours it was difficult 

 to tell the seat of the injury with the naked eye, and its diameter had 

 become reduced to one-half or one-third ; and after forty hours reco- 

 very was complete. He convinced himself by microscopic investiga- 

 tion that the process of regeneration of the epithelium proceeds from 

 the margins of the abrasion, the layers of cells immediately bounding 

 the seat of injury becoming elongated, and, as it were, sending forth 

 jjrocesses towards its centre ; so that the margins are rendered very 

 oblique, whilst at the same time the exj)oscd surface of the cornea is 

 raised considerably above the level of that which is still covered by 

 the cells. Sometimes the cell-processes become detached and contract 



