MICROSCOPY. 61 
out, than how they get out without leaving any trace of their pas- 
sage through the wall. Observers are agreed that both red and 
white corpuscles pass out of the vessels through apertures which, 
manifest during the period of transit, can be seen neither before 
nor after that time, and that it is essential to the process that the 
corpuscles shall cohere to the wall of the vessel and shall be sub- 
sequently subjected to pressure from within. The physical condi- 
tions essential to the passage of a rigid body through a colloid film, 
as when a solid body passes through a soap-bubble without break- 
ing it, are present in the case of the minute blood-vessels and the 
corpuscle, and are as follows ;—an intimate power of cohesion, ei- 
ther mediately or immediately, between the film and the body, a 
certain amount of pressure from within, and cohesive plasticity of 
the substance of the film so that the breach in it may become uni- 
ted as it descends upon the opposite surface of the body which is 
being extruded. 
Curring anD Staining Tissues.— Mr. E. Ray Lankaster recom- 
mends, in the “ Quarterly Journal of Microscopical Science,” that 
a small piece of tissue be enclosed in a metal box and frozen by 
means of a freezing mixture. It is then held between pieces of 
pith in wooden forceps (or an American clothes-peg) while sections 
are cut by a razor cooled in snow, the cutting being performed in 
acold room. Three razors are used that two may be cooled while 
one is used. The sections are first placed in a one-half per cent. 
gold chloride solution, or in silver nitrate solution if desired. 
After five to seven minutes they are transferred to distilled water 
and soaked for a few hours. They are then placed in’ water acidu- 
lated with lactic acid to reduce the gold chloride, and after the red- 
violet color is fully developed they are teased out, if oT ; 
and mounted in glycerine. 
ADULTERATION Or Tea AND Correre.— According to Dr. Hec- 
tor Helshan’s paper on the employment of the Microscope in 
analysis, before the South London Microscopical-and Natural His- 
tory club, coffee drinkers are liable to be treated to a decoction 
of roasted coffee-berries, chicory, poor flour, stale sea-biscuit, tan- 
yard refuse, peas, beans, and saw-dust. Some of these modern 
improvements may be escaped by buying the coffee unground. 
Dainty tea-drinkers will notice with interest that the Chinese ex- 
port teas rendered attractive by the salts of copper, lead, and iron, 
