Jan. 4, 1877] 



NATURE 



205 



Preparations are usually mounted in glass jars, open at the 

 top, and with a foot l)elow, and either circular or oval, i.e. 

 flattened on two opposed sides. The form is selected according 

 to that of the preparation. The ovals show off some preparations 

 to greater advantage than round bottles, but have the disadvantage 

 of being more expensive and being (especially when of large size) 

 liable to crack spontaneously, and apparently without provoca- 

 tion, but probably in consequence of some alteration of tempe- 

 rature affecting the unequal tension of the outer and inner surface 

 of the glass at the bent ends.' 



The fine silk threads by which the preparation is to be sus- 

 pended are brought over the edges of the jar, and passed benea'h 

 an ordinary thread tied round the groove, then returned and 

 ; secured across the top of the jar. As threads fastened in this 

 ■way occasionally are the means of causmg leakage of the spirit, 

 with which of course they are always sa'urated, some prefer to 

 tie them to a piece of wood, or whalebone, fixed across the 

 mouth of the jar. The only disadvantage of this is that it en- 

 tails some additional trouble, and a reducion of the number of 

 points of suspension which may be made use of in the other 

 method. 



There are two methods generally adopted for closing the upper 

 end of the jars after the preparation is mounted in it. The 

 oldest, and still very generally used, is by means of successive 

 layers of bladder, tin foil, thin sheet lead, bladder again. 

 and finally black varnish. The bladder must be macerated 

 until it is partially decomposed, and then it will adhere firmly 

 to the glass. This necessity makes the process a disagreeable 

 and dirty one. The object of the tin foil is to protect the lead 

 from the oxidisation which always takes p'ace when the vapour 

 of spirit comes in contact with it through the first layer of 

 bladder, tin not being so acted upon. A layer of tin only v;ould 

 answer as well as the tin and lead, but if thick enough for the 

 requisite strength, would be more expensive and less easily 

 ! worked round the edges of the glass. The thin sheet of tin 

 lis gummed to the surface of the lead, and then they are cut 

 I together to the requisite size, and treated as one, the tin being 

 j of course placed downwards. The edges are firmly pressed down 

 [round the lip at the top of the bottle and into the groove, with 

 pieces of box- wood shaped for the purpose. Much of the success 

 m closing the bottle depends upon the care with which this is 

 done. Then the second layer of bladder is put on, and tied 

 firraly with twine, round the groove at the top of the bottle. 

 When thoroughly dry the twine is removed, and the edges of the 

 bladder neatly trimmed with a knife ; it is afterwards coated with 

 one or two layers of black paint and a layer of black japan 

 varnish. 



Kottles closed in this way often keep in the spirit for many 

 years without any material alteration in its level, but there is 

 generally a slight evaporation, so that they have to be watched, 

 and whenever the spirit gets so low that the safety of the pre- 

 paration is endangered, the old cover must be cut off, and the 

 specimen remounted and closed in by the fame process. 



A more expeditious and cleaner process, which has also the 

 advantage of admitting light to the top of the preparation and 

 allowing it to be seen from above, is by the use of glass covers. 

 The top of the bottle is ground smooth, and a cover of glass 

 of thickness suited to the size of the bottle cut to fit it. Many 

 practical difficulties have been encountered in carrying out this 

 process, but they have been mostly surmounted by experiment 

 and perseverance, and it probably will in time entirely supersede 

 the bladder and lead plan. 



One cause of difficulty was the frequent breakage of bottles 

 so fastened, upon changes of temperature ; in the other plan, the 

 top, being somewhat flexible, yields v/ith the varying state of 

 expansion of the contents of the jar, but the glass top is per- 

 fectly rigid, and if the pressure is too great must either separate 

 from -the bottle or break. This occurs chiefly in large bottles 

 where the bulk of spirit is great, and consequently its expan- 

 sive power out of proportion to the strength of the gla^s. This 

 can be obviated to a great extent by not filling the bottle com- 

 pletely, as then the layer of air at the top, being far more 

 compressible than the spirit, acts as a sort of buffer between 

 the boMle and the glass ; but in large bottles we generally take 

 the further precauUon of a small safety-valve ; a hole drilled 

 through the cover, with a loosely fitting stopper to check too 



' Tlie greatest desideratum in putting u;) wet prepmations is a durable 

 glass jar with Hat sides, so that the distortion of the object caused by the 

 refraction through the curved surface of the glass may be avoided. Built up 

 cells do very well for small objects, but they are very expcibive, and geiier- 

 .-^'ly fail wh-jn tried on a large scale. The subject still offers a good field 

 for experiment. 



great evaporation, or the ingress of dirt. Through this bole 

 the jar can be filled up with spirit, when required, without the 

 necessity of disturbing the preparation, as in the old process. 



A second difficulty with glass-covered jars was to find a 

 cement to fix the top, at the same time easy of application and 

 not dissolved or weakened by the spirit. Isinglass dis'jolved in 

 strong acetic acid, pure gutta percha, a mixture of pitch and 

 gutta percha, and other substances, have been successively 

 used in the Museum of the College of Surgeons, but finally 

 we have given them all up for a composition sf>ld as " Rock 

 marine glue." ^ It is applied in a melted state, the edges of the 

 glass cover being also heated. A small gas jet fixed on a 

 flexible tube greatly facilitates this process. 



The suspending threads can either be fixed to a glass rod placed 

 across the top of the bottle just below the glass cover, the ends of 

 which are let into notches cut for the purpose on opposite sides 

 of the inside of the upper rim of the jar, or they can be brought 

 out between the top of the jar and the glass cover, embedded in 

 the cement, and secured by a string tied round the top of the 

 bottle till the cement is hard, when they can be cut off close to 

 the outer edge of the cover, and the securing string removed. 

 The preparation is then finished by neatly painting the edge of 

 the covering glass and cement, and the neck of the bottle for a 

 short distance below, with two or three coats of black varnish. 



For displaying different parts of the preparation, especially 

 canals or cavities, black and white hogs' bristles and variously 

 coloured glass rods are used. Delicate preparations, which cannot 

 be kept in position if simply suspended, are fastened by stitches 

 to thin transparent plates of mica, or to opaque coloured slabs 

 of wax, or cardboard. Black or blue are the colours generally 

 preferred, ps in greatest contrast to the usual colour of pre- 

 parations, as shown in the beautiful series of dissections illus- 

 trating the anatomy of the frog (3,904 f) contributed by Prof, 

 riuxley. 



I have said nothing yet about injecting preparations, a proce.'^s 

 necessary in order to display the course and distribution of 

 blood-ves-^els. There are two kinds of injections, fine and 

 coarse ; the former fills the capillary vessels, and for prepara- 

 tions intended to be seen with the naked eye, gives a blush of 

 the colour used to the tissue, and is chiefly valuable as indicating 

 the relative amount of vascularity of contiguous tissues. For 

 microscopical investigations it is invaluable, and the methods 

 employed and the materials used are fully detailed in all works 

 devoted to microscopical manipulation. Coarse injection is 

 intended only to show the vessels visible to the eye, and not to 

 enter into the capillaries. Size, so generally used as a basis for 

 fine injections, is not so satisfactory in this case, as if in any 

 bulk it contracts in the spirit. The best material (intro- 

 duced by Dr. J. B. Pettigrew, F. R.S., when Assist ttu m the 

 Museum of the College of Surgeons) is fine plaster of Paris, 

 coloured with vermilion or ultramarine, according as the tint 

 of red or blue is required. It is mixed with water, as in 

 taking casts, though of rather a more fluid cons'stence, and 

 of course must be injected immediately, or it will set in the 

 syringe. It has the great advantage of being used cold. It is 

 rather brittle when set, and the vessels should be handled with 

 care, but it may be made more tenacious l.'y the addition of some 

 glue or isinglass to the water with which the plaster is mixed. 



The distinction between two different kinds of tissue is some- 

 times well shown by staining the preparation. Some good 

 examples are exhibited by the Anatomical Museum of the Uni- 

 versity of Oxford. The head of a stu'geon (Nos. 3,837 and 

 3,838, prepared by Mr. Robertson) has been immersed for a 

 short time in a solution of carmine, and the carii'age and connec- 

 tive tissue has received the colour, while the bones retain their 

 natural white hue. The distinction between them, which other- 

 wise would scarcely be perceptible in the bottle, is thus very 

 clearly brought out. 



The third and last great division of museum specimens for 

 teaching purposes, illustrated by this exhibition, is that which 

 comprises models and casts of natural objects, and under the 

 same heading drawings and diagrams may be included. 



As a general rule, models should never be used for teaching 

 if actual specimens can be obtained and exhibiied ; but there 

 are numerous cases in which the object is of so perishable a 

 nature, that it cannot be preserved efficiently by any of the 

 methods above described. Many objects are so scarce that 

 it is quite out of the power of most museums to pos-;e^". any 

 representations of them, except as copies of the originals. 



* It is bought from Rockhill and Co., to, Blackfriars Road. 



