204 



NATURE 



{Jan. 4, 1877 



MUSEUM SPECIMENS FOR TEACH IMG 

 PURPOSES^ 



III. 

 T NOW pass to the second great division of museum prepara- 

 *• tions, those that are preserved in a fluid medium ; the only 

 wky in which the greater part of the structure of most animals, 

 both vertebrate and invertebrate, can be kept from change and 

 decomposition. _ . „ , ^ 



The first question for consideration is the best preservative 

 medium. The one which has been most extensively used iii 

 all countries is alcohol. Various substitutes, as solutions of 

 common salt, alum, bichloride of mercury, or arsenic, have been 

 proposed and tried, chiefly on account of the expense of alcohol, 

 and other slight disadvantages, but after a few trials these have 

 eenerally been given up. At all events, the experience of alcohol 

 in all the large museums of this country, has been so satisfactory 

 compared to that of other media, that it is now alone used. The 

 objection of expense which was caused by the high duty, has 

 betn in a great measure obviated by the permission to use "methy- 

 lated " spirit, duty free, though some disadvantages have been 

 thereby entailed.* , , , . , r 1 i, 1 j 



There seems little doubt but that a mixture of alcohol and 

 water (commonly known as " spirits of wine," or when spoken 

 of in relation to anatomical purposes, as "spirit only) ot the 

 proper strength will preserve an animal substance for an inde- 

 finite length of time. There are specimens in the exhibition, 

 (No 3878 a), belonging to the Museum of Anatomy of the 

 Academy of Science at St. Petersburg, prepared by the cele- 

 brated Dutch anatomist Ruysch, and bought from him by the 

 Czar Peter the Great, in 171 7, still in a perfect state of pre- 

 servation. We have now in the Museum of the College of 

 Surgeons many thousand preparations put up in the last century 

 by John Hunter, and which appear to have undergone no 

 changes beyond those which took place during the first few 

 weeks of immersion in spirit, and which may be described as 

 a certain amount of hardening and contraction of the tissues by 

 coagulation of the albumen contained in them, and discharge of 

 much of the natural colour. 



The extent to which these changes take place depends very 

 much upon the method with which the specimen is treated in the 

 first instance. Sometimes it is desirable to harden the structure 

 rapidly, as in preparations of hollow viscera, when the form 

 alone is essential, in others, where preservation of the general 

 appearance and the texture of the tissue is more requisite, and 

 where further dissection is likely to be required, it is best to keep 

 it as much as possible of the natural softness. The first condi- 

 tion is produced by immersing the preparation, when placed in 

 the position in which it is to remain, in alcohol of the greatest 

 strength, which afterwards may be diminished ; the latter by 

 beginning with a weak solution and gradually increasing the 

 strength up to that finally used for permanent preservation. 



The strength of the alcohol is estimated by its specific gravity, 

 ascertained by the instrument called the hydrometer. But we 

 do not speak of the actual specific gravity of physicists, but 

 follow the conventional standard of the spirit-trade, the starting- 

 point being taken at what is called "proof" at a temperature of 

 60" F., and the scale divided into degrees or " per-centages 

 above and below proof. By i percent, or I degree under proof, 

 is meant proof spirit with one-hundredth part (by bulk) of water. 

 Spirit 10 per cent, under proof is a spirit consisting of 90 parts 

 of proof spirit and 10 of water. On the other hand, by 40 per 

 cent, over proof is meant that lOO parts (by bulk) of such spirit 

 will require 10 parts of water to bring it to proof. 



The "rectified spirit," as commonly sold, is about 60 or 65 

 per cent, above proof. This is only used for hardening prepara- 

 tions. , . . . t 



For ordinary use in the museum, proof spirit is stiong enougn, 

 though to be quite on the safe side we generally use 10 per 

 cent, over proof, diluting the rectified spirit with distilled water 

 till it is reduced to the requisite strength, as ascertained by the 



' Lecture at the Loan Collection of Scientific Apparatus, South ICen- 

 siiiBton, July 26, 1876, by Prof. W. H. Flower, F. R. S., Conservator of the 

 Museum of the Royal College of Surgeons of England. Continued from 



^'Methylated spiiit is decidedly inferior in transparency and in ahsence •f 

 colour to pure spirit, .md even if bright when first used, is apt to become 

 turbid afier a time. In a large esiabhshment this can be to a great extent 

 remtdied by passing the' discoloured spirit through a still, but it would 

 be very desirable to consider whether some other method could not be 

 devistd by which alcohol could be used for scientific purposes, without the 

 necessity of paying the present heavy duty of sixteen shillings and sixpence 

 « galloa. 



hydrometer. This is the strength commonly used for all kindi 

 of preparationSj though it might ,be varied with advantage m 

 some cases. 



In estimating the preservative power of spirit, consideration 

 should be given to the bulk of the specimtil, and especially the 

 amoiint of water contained in its tissues, as compared with the 

 quantity of spirit used. For instanct, if a large solid mass of 

 animal substance is placed in a jar httle lafgfer than sufficient to 

 contain it, filled up with proof spirit, the amount of fluid coii- 

 tained in the specimen will so dilute the spirit that decomposi- 

 tion, especially of the interior of the specimen, to which thft 

 spirit cannot penetrate, will not be prevented, whereas a smaller 

 specimen placed in the same jar of spirit will be preserved per- 

 fectly. Many collectors of objects of natural history do not 

 attend sufficiently to these considerations, and hence the speci- 

 mens become spoiled, much to their disappointment ort) that of 

 their consignees. The way to obviate this is not to use stronger 

 spirit, as thac would harden the exterior of the specimen, and 

 prevent the spirit penetrating to the centre, but to use 

 greater bulk of spirit, and especially to change it, after a day or 

 two, pouring away the old diluted spirit, and substituting 

 fresh, repeating the process if necessary more than once. 



When a specimen has once been thoroughly saturated with 

 spirit, and its tissues hardened, a strength much below proof will 

 be sufficient to preserve it. The nature of the specimen must 

 also be taken into consideration. For instance, nerve tissue, as 

 in the brains of animals, requires stronger spirit for its preserva- 

 tion than ligamentous or fibrous ti?sues. Much will also depend 

 upon the freshness of the specimen. If decomposition has 

 already set in Defore it is placed in spirit, it will require much 

 stronger spirit, and more frtquent renewals than if it is fresh. 



With most preparations it is desirable to cleanse them well 

 before mounting them in spirit. They should be left a few hours 

 or days (according to the temperature) in water frequently re- 

 newed, and the blood should be washed out of the large vessels, 

 by means of a stream of water directed through them. This 

 will save to a large extent the discoloration of the spirit into 

 which they are placed. When removed from the water they 

 should be allowed to drain, and be gently dried with a cloth 

 before placing in the spirit, but no part of them must on any 

 account, at any time during the process of preparaiion, be allowed 

 to become actually dry, otherwise dark stams which are quite 

 irremovable will be produced. This precaution is most essential 

 when they have been once in spirit, and are removed for exami- 

 nation or further dissection, as evaporation of the alcohol, and 

 consequent desiccation of the preparation, takes place much more 

 rapidly than that of water. 



In most cases it will be requisite to change the spirit once Or 

 oftener, before all the soluble colouring matter is given off from 

 the preparation, and it can be permanently mounted. The 

 discoloured spirit need not be wasted, as it can be perfectly 

 restored by passing through the still. 



To succeed in making a good anatomical preparation, much 

 patience, neatness of hand, knowledge of the subject illustrated, 

 and some atrtistic talent are required. No pains should be spared, 

 to make it tell the lesson it is intended to convey in the most 

 attractive and pleasing manner. Everything should be displayed 

 as definitely and clearly as in a drawing, and there should be no 

 appearance of negligence or want of finish in any part. 



When an elaboiate dissection is required, it must, at least ih 

 all its "later stages, be carried on while the specimen is under 

 spirit, fixed in a flat dish or basin. The small fragments of con- 

 nective tissue which have to be removed then float out frofti 

 between the fibres of the muscles and the vessels which are to be 

 preserved and exhibited, and they are carefully snipped off with 

 fine curved scissors. A dissection which looks clean and highly 

 finished as long as it is in air, when placed in fluid, becomes at 

 once cloudy and obscure, from the floating up of these litde 

 particles. Hollow viscera, as hearts or stomachs, are distended 

 by injecting their interior with strong spirit, tying or plugging 

 the apertures by which it could escape, and placing them f^or 

 several days in a vessel with the same fluid. If all the requisite 

 precautions are taken, they will then preserve their form, and 

 the interior of their cavities can be exhibited, by cutting openings 

 or "windows" through different parts of their walls. If from 

 any cause a cavity cannot be made to contain spirit, it may be 

 stuffed with cotton-wool or horse-hair during hardening. The 

 preparation, when laid aside to harden, if not suspended, should 

 be placed in a bed of cotton wool adapted to its form, other- 

 wise it will become irremediably flattened on the side on which 

 it rests. 



