ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 659 



stained preparations of nerve-tissue, the author squeezes a piece of grey 

 substance about the size of a hemp-seed between two cover-glasses. The 

 double cover is then placed for 15 days in picrocarmine, four days in 

 absolute alcohol, and then for two days in oil of cloves and xylol apiece, 

 and lastly fixed up with xylol dammar, which is poured over the cover- 

 glasses. After the dammar varnish is dried the surface of the cover- 

 glass is cleansed of the resin. 



New Method for the Microscopical Study of the Blood.* — The 

 methods hitherto employed in preparing the blood for microscopical 

 examination have aimed either at the production of fresh or of dry pre- 

 parations. Preparations of the first class are not permanent, and those 

 of the second class never exhibit the morphological elements intact. 

 Dr. D. Biondi has worked out a method which combines the advantages, 

 and is free from the defects, of previous methods. The problem was to 

 find the means of perfect fixation, preservation, imbedding, and mounting 

 — in other words, a method by which the blood could be treated as a 

 solid tissue. The method is equally useful in the study of other organic 

 fluids, and has been successfully employed in tracing the changes that 

 take place in the maturation of the spermatozoa. It may doubtless be 

 used to advantage in the study of Infusoria, as suggested by Biondi. 



The point of chief interest in Biondi's method is the use of agar as 

 an imbedding material. Agar is a vegetable gelatin obtained from 

 Gracilaria lichenoides and Gigartina speciosa, and has already been 

 successfully emj)loyed for some time by Koch in bacteriological investi- 

 gations. Among the different sorts of agar, the columnar form (Saulen- 

 Agar) is considered the best. A perfectly transparent solution is 

 required, in the preparation of which great care must be taken. This 

 may be accomplished in the following manner : — Place two parts of 

 agar in 100 parts of distilled water, leaving it to soften for twenty- 

 four hours at the ordinary room temperature ; then heat to boiling on the 

 sand-bath until the agar is all dissolved. The evaporation of the water 

 may be checked by closing the flask with a cork provided with a long 

 glass tube. Add carbonate of sodium to the point of weak alkaline re- 

 action, and boil for an hour in a steam apparatus. Pour the solution 

 into long slender test-tubes, and leave from 12-24 hours at a temperature 

 of 50° to 60° C. The solution separates into two layers, the upper of 

 which is quite clear, and this layer alone can be used for imbedding 

 purposes. But clarification must be carried still farther before it is fit 

 for use. The clear portion of the solution is next to be heated to about 

 40°, white of egg added, the mixture shaken up several times in the 

 course of ten minutes, boiled for an hour in the steam apparatus, and 

 then filtered. The reaction should then be tested, and, if necessary, 

 carbonate of sodium added until the solution is neutralized. Exact 

 neutralization is necessary, in view of the staining fluid to be employed.| 



It is important that the mass should be kept sterile up to the moment 

 of using, as otherwise a large number of micro-organisms may develope 

 in it and render it worthless for the finer uses. It is advisable, there- 

 fore, to keep the mass in test-tubes, limiting the quantity placed in each 

 to the probable requirements of a single imbedding operation. For a 

 single preparation of the blood five cmm. of the mass is sufficient. The 



* Arch. f. Mikr. Anat, xxxi. (1887) p. 103. Cf. Amer. Natural., xxii. (1888) 

 pp. 379-81. 



