150 SUMMAEY OP CURRENT RESEARCHES RELATING TO 



tubes to remove the alcohol and washings. For producing trans- 

 parency, oil of cloves has been used, and the mounting has been 

 done under thin, clear covers, in a solution of Canada balsam in 

 chloroform. 



All the negatives have been made on glass thoroughly cleaned 

 and lightly coated with a solution of wax and benzole, so that the 

 collodion film, previously made adherent to thin sheets of gelatine, 

 could be safely removed from the plate. The flexible negatives thus 

 obtained are well adapted to the artotype process, and, as they can 

 be indefinitely preserved betwesn the leaves of an ordinary scrap- 

 book, are very desirable for a series of illustrations. In making the 

 original negatives on glass, the ' wet collodion process,' with the 

 sulphate of iron developer, has been exclusively employed. 



The prints correspond exactly with the negatives, both in outline 

 and detail. No distortion occurs as in silver printing, in which 

 process the paper is subjected to prolonged washing. 



In many of the photographs the grey substance appears lighter 

 in shade than the white substance. This appearance is due to a 

 greater degree of transparency of the grey substance in these sec- 

 tions, resulting from the action of the oil of cloves, followed by an 

 increased action of the transmitted light on the sensitive collodion 

 film of the negative, and hence by a thinner deposit of ink over 

 corresponding parts of the positive plates from which the artotypes 

 are printed." 



With regard to the process employed, Dr. Mason says that after 

 experimenting with various methods he found that satisfactory prints 

 could be made in ink directly upon plate paper, and that these im- 

 pressions were as perfect in fine detail as any of those obtained by 

 the silver process of printing. The plates (all printed by the arto- 

 type process) are as durable as steel engravings. " While a photo- 

 graph cannot often show all that can be discovered by more direct 

 microscopic observation with a judicious working of the fine adjustment, 

 high authority has stated, and perhaps correctly, that a good photo- 

 graph with a low power — say from 3 to 1/2 in. — is a better means of 

 illustrating the anatomical structure of the nervous tissues than hand 

 drawing. Some of the plates with high powers leave much to be 

 desired both in distinctness and tone, and in general it may be 

 affirmed that the same defect as regards distinctness always exists, 

 and for obvious reasons, in photographs of sections with powers much 

 above 1/2 in. In fact it now appears to be established that immer- 

 sion objectives can never be employed for photographing section- 

 preparations with the success that has attended their use for blood 

 corpuscles, diatoms, and similar specimens." 



Preparing Spermatozoa of the Newt.* — G. F. Dowdeswell writes 

 that to prepare the spermatozoa of the newt for the examination of 

 the minute barb discovered by him, the first essential is to get them 

 as nearly as possible in contact with the cover-glass and flat upon it ; 

 this requires some care to avoid their drying, by which they are 



* Quart. Journ. Micr. Sci., xxiii. (1883) pp. 336-9 (1 fig.)- 



