380 General Notes. 
red. 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 develop in it, and render it worthless for the finer uses. It 
is advisable, therefore, 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 
ccm. of the mass is sufficient. The test-tubes should be cleansed 
with hydrochloric acid and then washed with distilled water. After 
receiving the agar solution, the tubes are closed with cotton, and 
then sterilized in the steam-apparatus for half an hour daily on 
three successive days. 
As the preparation of the agar mass is somewhat complicated, 
much time and trouble may be saved by turning this work over to 
some apothecary. König of Berlin (Dorotheenstrasse, 29) furnishes 
the mass prepared as above described. 
The best medium of fixation for the elements of blood is a 2 per 
cent. solution of osmic acid. If a drop of blood from the frog be 
examined in this medium under the microscope, it will be seen that 
_ both the red and the white corpuscles are perfectly preserved in 
form and structure. The red corpuscles become a little paler than 
in the living condition, and are slightly browned. The corpuscles 
of mammalian blood are isolated and seen to greater advantage 
than in any other medium of fixation. As it is important that the 
acid should be perfectly clear and free from all impurities, it is well 
to filter before using. 
Method of Procedure.—1. By the aid of a clean pipette, take a 
little blood from the heart of a frog, and allow two drops to fall 
into 5 ccm, of osmic acid (2 per cent.). Shake a little—the sooner 
the better—in order to separate the elements and scatter them 
through the whole body of the acid. After standing awhile, the 
blood corpuscles will be found at the bottom of the tube, the deeper 
layer being formed mainly of red corpuscles, which sink first by 
virtue of their greater specific gravity. Exposure, one to twenty- 
four hours. ‘ 
2. The process of fixation completed, 4 to 5 drops of the mix- 
ture of blood and osmic acid are allowed to fall from a pipette 
into the melted agar, which is kept fluid at a temperature of 35 
to 37°C. By rotating the test-tube, the blood corpuscles are dis- 
tributed through the agar, and then the whole is poured into & 
aper box, as in the ordinary paraffine method of imbedding. 
Within a few minutes the mass stiffens, and may be removed from 
the box to 85 per cent. alcohol for hardening. In three to SIX 
