50 THE AMERICAN MONTHLY [ March, 
clearing sections in which the presence of the celloidin is essential to the in- 
tegrity of the section; for example: in clearing porous specimens, speci- 
mens consisting of loosely-united lamellz, serial sections prepared by the 
method of Weigert, in which the series are held in place between two thin 
adherent films of celloidin. Among the oils which do not dissolve celloidin 
from the section, in clearing, thyme and origanum are commonly employed. 
Owl of Thyme—Thymus vulgaris.—A large part of the oil of thyme of 
commerce is made in southern France from the cultivated plant. There are 
two varieties—white and red. The white oil is made by rectifying the red 
variety.* The disadvantages of both of these varieties, in clearing, are :— 
1. The sections require very thorough dehydration ; in damp weather abso- 
lute alcohol must be used. 2. The celloidin frequently remains clouded for 
some time after the section is clear, and is much folded and corrugated. 
3. These oils contain an acid holding oilf which *fades the copper hema- 
toxylin preparations of Weigert, if the section remains in the oil from one to 
two hours; or, if the sections are removed from the oil as soon as possible 
and mounted in balsam, they frequently fade in a few days. The white 
French oil of thyme clears specimens much more readily if a small quantity 
of absolute alcohol is added to it. To obviate the objections to oil of thyme, 
Minot and Dunham} suggest diluting it with from # to } of its volume of oil 
of cloves. In our experience this mixture very frequently fades the copper 
hematoxylin preparations of Weigert. There is a second variety of oil of 
thyme made from the uncultivated plant, known as Oleum Serpyllum— 
Thymus Serpyllus. ‘This is open to the same objections as the French oils. 
Oil of Origanum.—There is some confusion in this country about this 
oil, for the reason that oil of thyme has largely been substituted for oil of 
origanum.§ With some of the dealers the terms ‘ origanum’ and ‘thyme’ are 
used synonymously, and most of the samples purporting to be origanum are 
simply the pure French oils of thyme or the impure grades diluted with vary- 
ing proportions of turpentine. This is notably the case with the reddish 
brown commercial varieties of these so-called ‘ oils of origanum.’ Hager|| 
mentions two varieties of the true oils of origanum :—1. Ol]. Origani Cretici, 
Spanisch Hopfen-dl. 2. Ol. Origani Gallicum. The first of these does not 
dissolve celloidin in clearing, and is far superior to oil of thyme. It clears 
sections rapidly even in moist weather after their dehydration in 950 alcohol. 
It sometimes folds the edges of the celloidin to an inappreciable extent. It 
is free from acid and does not fade sections stained by Weigert’s hamatoxy- 
lin method if the preparations are hardened for a long time in Mueller’s fluid, 
and are subsequently mounted in thick balsam. Specimens containing bac- 
teria, stained by either Gram’s method or the simple anilin colors, may be 
cleared by this oil without fading. It does not remove the color from hema- 
toxylin and eosin-stained specimens. 
When the sample is freshly opened it has a light amber colorand does not 
clear readily, but after it has been exposed to the air for some time and a num- 
ber of sections have been cleared in it, it becomes darker in color and clears 
without difficulty. Among the makers of this oil of origanum the house of 
Schimmel & Co. is to be preferred. It has but recently been imported to 
this country, and may be obtained of their agents, Fritsche Bros., Barclay 
st., New York. 
Anilin Ozl.—Merck’s anilin oil clears sections readily and leaves the cel- 
loidin intact and pliable. It changes the tint of eosin-stained specimens 
slightly. It does not fade the Weigert hematoxylin staining, and may also 
* Pfliickiger and Handbury Pharmacographia, ’79. + Hager, Pharmaceutische Praxis, vol. ii. 
{ Zeitschrift fiir Wissenschaftliche Mikroscopie tind fiir Mik. ‘Technik, Band iii, vol. ii. 
§U.S. Dispensatory, 83. || Op. Cit., vol. ii. 
