52 



TRANSLATIONS. 



On the Distinguishing of Elevations and Depressions 

 under the Microscope. By Dr. H. Welcker. 



( 4 Zeitsch. f. ration. Medicin,' 3 ser., Bd. vii, p. 63, 1859. 



It cannot be contested that the most important point in 

 every microscopical investigation is the correct interpretation 

 of the visible image presented to us. But, as in the latest 

 classical work by Dr. Harting (' Das Microskop, ' &c.) the 

 subject of Microscopic Diagnosis does not appear to me to 

 have been treated so fully or so correctly as it might have 

 been, I venture to recur to the subject, which has already 

 been noticed by me in papers on Microscopic Technology 

 formerly published in this Journal.* 



I. On Diagnosis by oblique illumination. 



Dr. Harting considers that minute elevations and depres- 

 sions on microscopic objects may be readily confounded, 

 owing to the circumstance that each is indicated under both 

 transmitted and direct light by a shadow (Schlagschatten), 

 which may be exactly alike in either case ; but whose posi- 

 tion as regards the source of illumination does not in micros- 

 copic vision immediately indicate the true form of the 

 object, as it does in ordinary vision, — for the reason, that the 

 requisite point of comparison is, in the former case, more or 

 less wanting. But in the compound microscope a deception 

 may more readily arise "because the whole image here 

 appears inverted, and the shadows consequently fall in a 

 direction opposite to the true one ; — that is to say, in the case 

 of an elevation they are directed towards the source of light, 

 and the reverse in case of a depression." 



* ' Zcits. f. rat. Med.,' 2 ser., vi, p. 172, and viii, p. 241. 



