Dr. F. A. Bather—Collodion Imprints of Fossils. 437 
IIT.—Narnorst’s vst oF Coztoprion Imprints IN THE Srupy oF 
Fossit Pants. 
By F. A. Barurr, M.A., D.Sc., F.G.S., British Museum (Natural History). 
HE following note is based on two papers by Professor A. G. 
Nathorst! and on further details which he has kindly communi- 
cated by letter. For the loan of the block (Fig. 1) thanks are due 
to Dr. H. Munthe, Secretary of Geologiska Foreningen i Stockholm. 
By the term ‘collodion imprint’ is meant the impression of any 
surface on a thin film of collodion. Such an impression is obtained 
by letting a drop or two of collodion dissolved in ether fall on the 
surface to be copied. The ether evaporates rapidly, so that in two or 
three minutes the film is hard. If it does not of its own accord come 
loose at the corners, it is easily raised by a needle or sharp knife. It 
is then lifted on to a glass microscope-slide and preserved dry under 
a cover-slip held in position by gummed strips of paper or by Canada 
balsam. When the imprint is very sharp, the film. can, if desired, be 
preserved in glycerine-jelly without its distinctness being greatly 
affected. Some films may be less successful than others, and some 
may curl too much, so that it is as well to take more than one 
imprint. In any case it is advisable to throw away the first made, 
since it usually retains some dust from the surface of the object, 
whereas following films will be free from this. If the collodion 
solution is too thick it may be thinned by the addition of ether or of 
ether and alcohol. The thicker the solution, the more liable is it to 
air-bubbles; the thinner solution gives a thinner and clearer film, 
which may sometimes be an advantage, also it takes longer to dry, 
which is of no great consequence. No definite prescription can be 
given as to thickness; one must find out for oneself the kind of 
solution most suitable for the objects with which one is dealing. 
The film placed on the slide is examined under the microscope by 
transmitted ight. Since the film is thicker over the depressions of 
the original surface, it appears darker over these tracts, so that the 
structure is easily seen. In fact, quite high powers of the microscope 
can be used, and photomicrographs taken. Professor Nathorst repro- 
duces one such photograph with a magnification of 500 diameters (Fig. 1). 
The illumination of the film should not be directly from below, but 
oblique, the mirror being shifted until the best effect is obtained. 
Such collodion films have long been used in the measurement of 
microscopic objects, especially in the preparation of copies of the eye- 
piece-micrometer in order to determine the magnifying power of the 
microscope. They have also been employed by botanists to copy the 
cuticular surface of living leaves for the study of physiological pro- 
cesses.” L. Jost also briefly stated in 1902 that he had successfully 
1 “ Kollodiumaftryck sésom hjilpmedel vid undersékning af fossila ,,vaxter’’: 
Geol. Foren. Férhandl., Bd. xxix, pp. 221-227, April, 1907. ‘‘Uber die 
Anwendung von Kollodiumabdriicken bei der Untersuchung fossiler Pflanzen”? : 
Arkiy for Botanik, Bd. yi, No. 4, 8 pp., 1 pl., August, 1907. 
2 L. Buscalioni e G. Pollacci: ‘‘ L’applicazione delle pellicole di Collodio allo 
studio di alcuni processi fisiologici nelle piante ed in particolar modo alla Tra- 
spirazioni,’’? and ‘‘ Ulteriori ricerche sull’ applicazione, etc.’’: Atti dell’ Istituto 
botanico dell’ Universita di Pavia, ser. 11, vols vii, Milan, 1902. 
