306 PROFESSOR LISTER ON THE GERM THEORY 
the scum of the earlier period, so that the specific identity of the two growths 
was no longer doubtful. 
I afterwards obtained still more satisfactory evidence on the same point. 
The long sprouts observed in the scum of the second glass of urine, a few hours 
after inoculation, seemed to indicate that the very liquid which, when altered 
by fermentation, induced the change of the organism to the toruloid condition, 
favoured, when perfectly fresh, a return to the filamentous form. I therefore 
resolved to watch, if possible, the earliest growth of the spherical cells of the 
scum in uncontaminated urine. For this purpose I proceeded on the same 
principle as before; but experience having shown that the thin layer of atmo- 
sphere between the glass plates was exhausted within a few hours, I tried a new 
arrangement for providing a larger supply of air, that which I ultimately arrived 
at being as follows:—A piece of plate-glass about ths of an inch thick, and 
} about 24 inches by 13 in the other 
dimensions (shown in diagram in the 
accompanying woodcuts, the lower 
of which represents it in section), is 
excavated by the lapidary into a 
circular ditch, D, round a central 
island, I, the island being ths of an 
inch in diameter, and the ditch or air 
chamber of about the same breadth, 
and as deep as the thickness of the 
_E BO glass will conveniently permit, viz., 
about a quarter of aninch. A piece 
of thin covering glass, P, sufficiently large to cover the ditch as well as the 
island, but not quite so broad as the glass plate, so that it can be conveniently 
sealed down with paraffin, completes the “ glass garden,” * which is stocked as 
follows:—The glasses must first be heated and allowed to cool, without access 
of dust to the air-chamber. The glass plate with the cover wm situ, and covered 
further with a rather larger slip of ordinary glass, is placed upon a broad 
plate of metal on a retort stand, and over this a metal lid, such as that of a 
tin biscuit-box. Heat is then applied to the metallic plate by means of a 
BunseEn’s burner or large spirit-lamp, till a drop of water sprinkled on the tin 
lid above passes off at once by ebullition. The lamp is then removed, and cooling 
is allowed to take place completely. The object of the metal plate and lid is to 
diffuse the heat, and thus prevent cracking of the thick and irregularly-shaped 
plate of glass. The lid above aids in keeping out dust during cooling, and this 
is further effected by the thin covering glass and the overlapping glass slip 



* Such glass gardens may be obtained of Messrs Sanpersoy, lapidaries, 92 Princes Street, Edin- 
burgh. 
ee Fe ai a ee ee ee 


