ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 143 



silver, and warmed. To this is added a very small quantity of an 

 aqueous solution of pyrogallic acid, whicli reduces the silver in a few 

 seconds ; chloral and glycerine are added as before. It does not 

 change either in alcohol, chromic or acetic acid, or in bichromate of 

 potash, &c., so that the objects can be hardened in different fluids. 

 Blue and yellow masses mixed give a very useful green. 



Prof. Hoyer recalls attention to two other formulae previously 

 described by him,* but " which have not received any notice in histo- 

 logical text-books." The one is ammonio-nitrate of silver, especially 

 suitable for the endothelium of vessels and fine vessels generally, and 

 much to be preferred to the simple nitrate of silver solution. The 

 other is spirituous solution of shellac. 



Taylor's Freezing Microtome.| — This microtome (fig. 29), the 

 invention of Dr. T. Taylor, Microscopist of the Agricultural Depart- 



ment at Washington, is claimed to present " all the advantages of 

 any plan heretofore employed in hardening animal or vegetable 

 tissues for section cutting, while it has many advantages over all 

 other devices employed for the same purpose. 



Microscopists who are interested in the study of histology and 

 pathology have long felt the necessity for a better method of freezing 

 animal and vegetable tissue than has been heretofore at their 

 command. In hardening tissues by chemical agents the tissues are 

 more or less distorted by the solutions used, and the process is very 

 slow. Ether and rhigolene have been employed with some degree of 

 success, but both are expensive and they cannot be used in the 

 presence of artificial light because of danger of explosion. Another 

 disadvantage is that two persons are required to attend to the 

 manipulations, one to force the vapour into the freezing box while 

 the other uses the section-cutting knife. The moment the pumping 

 of the ether or rhigolene ceases, the tissue operated on ceases to 

 be frozen, so ephemeral is the degree of cold obtained by these 

 means. 



* Arch. f. Mikr. Anat., xiii. (1877). 



t Amer. Mon. Micr. Journ., iii. (1882) pp. 168-9 (1 fig.). 



