204 Dr. J. B. Haycraft. 



a layer of uniform thickness. When still somewhat moist I pressed 

 against the film some roughly teased muscle fibres held on my finger 

 tip. They came away quite readily when the finger was removed, 

 leaving little " rnta " in the collodion obvious to the nnaidod eye. On 

 examining these ruts with the microscope I found what I at first 

 thought were actual muscular fibres still adhering to the collodion 

 film, showing the fibrils and every detail of the cross striping with 

 remarkable clearness. The ruts contained, however, no trace of 

 muscular tissue when examined by the naked eye, for the slightest 

 trace of muscle is at once recognised by its opacity. On looking at the 

 specimen a few minutes afterwards, what was my surprise to find that 

 all the appearances I had just seen had completely vanished, the ruts 

 had disappeared, and the collodion film was flat and smooth. 



The explanation was very soon found, and no doubt remained 

 that what I had at first actually mistaken for muscular fibres were it 

 reality their " impressions," their subsequent disappearance beinj 

 due to the contraction of the film, as it dried, pulling out every in- 

 equality in its surface. 



It is very instructive to watch one of these collodion impressions ; 

 at first clearly cut, with every stripe sharply defined, they gradually 

 fade, and perhaps in five or ten minutes they disappear entirely. 

 Sometimes a portion of a fibre really remains sticking to the col- 

 lodion ; it is at once recognised by its great opacity. What astonished 

 me almost as much as the perfect reproduction in the impression of 

 every cross stripe was the ease with which these impressions can be 

 made. One can hardly fail to obtain them, and at the International 

 Congress in Berlin, while demonstrating the subject to the members 

 of the Physiological and Anatomical Sections, I made over one hun- 

 dred preparations few of which were failures. Not only can one 

 stamp with hardened muscle, but the fresh tissue can itself be used. 

 Of course the fresh tissue is soft and does not make so good a stamp, 

 the results are not so striking, but they are quite evident. In making 

 impressions of a fresh muscle one can take a piece of muscle, say 

 from a Rabbit, cut it through in the direction of the fibres, and press 

 the cut edge for a second or so against the collodion film, which must 

 be very soft : one rarely examines the film without getting some trace 

 of an impression upon it.* 



If the impressions are examined with a high power, say 600 diameters, 

 the following details can be made out. Each fibril, if a hardened 



* One can get impressions of other tissues, bone, tooth, hair, &c. A section of 

 dry bcne comes out Tery well, and one can see in the impression the " set " of the 

 lamellae, the lacunae and their canaliculae, and every detail with marvellous clear- 

 ness. If a still moist film be pressed against the back of the hard, and then ex- 

 amined, one sees the impressions of the imbricated scales covering the hairs on 

 back of the hand far clearer than in the original. 



