Photographing Histological Preparations hy Sunlight. 169 



to convey the appearance of objects in motion ; however impressive 

 may be their appearance, the onward procession is but an optical 

 illusion ; I assume therefore that for the instant they are fixed when 

 by the employment of linear projection the individual positions of 

 the cilia are found to be as indicated on the drawing, which I sub- 

 mit is correctly represented, and shows more clearly and truly the 

 actual appearance assumed in life. 



II. — On an Improved Method of Photographing Histological 



Preparations hy Sunlight* 



By J. J. Woodward, Assistant-Surgeon, U. S. Army. 



General : In January, 1870, I had the honour to submit to you a 

 report in which I detailed the results of a series of experiments, 

 which showed the superiority of the Electric and Magnesium lights 

 over sunlight, as heretofore employed, for the production of photo- 

 micrographs of the soft tissues. In June of the same year I made 

 a report in which I showed that similar results could be obtained 

 with the Oxy-Calcium light. With these various artificial sources 

 of light I obtained pictures which appeared to me to be " clearer 

 and better defined than any photographs of similar objects I had 

 hitherto seen produced by sunlight." 



So many cloudless days are ofiered to the photographer in 

 Washington that I could not but regret these results; yet they 

 appeared to be final at the time of writing. During the last few 

 months, however, I have found improved methods of using the light of 

 the sun for photographing the soft tissues, and have arrived at results 

 which must materially modify the conclusions of my former reports. 



Not that I have anything to withdraw from the opinions 1 have 

 expressed, as to the certainty and success attending the use of arti- 

 ficial lights for the purpose named, but I have much to add with 

 regard to the most advantageous methods of using the hght of the 

 sun for obtaining satisfactory pictures of tissue preparations, and 

 such other objects as approximate them in optical characteristics. 



If a well-made preparation, of some normal tissue, or of some 

 pathological growth, stained with carmine, silver, or gold, and 

 mounted temporarily in glycerine, or permanently in Canada balsam, 

 be illuminated by white cloud illumination, or by lamphght, and 

 found to be all that could be desired, it will nevertheless appear very 

 unsatisfactory if illuminated by the direct rays of the sun. 



The eye glancing through the tube of the instrument, dazzled by 

 the powerful hght, discerns amidst the blaze innumerable coloured 



* The report is made to Brigadier-Geueral J. K. Barnes, Surgeou-General 

 U. S. Army. 



