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MlCllOSCOPE, USES OK TIIK. 



MICROSCOPE, USES OF TIIK. 



&!* 



having Won previously cleaned and warmed, may then I* taken in a 

 pair of forceps, and, after being held over the warm balsam for a 

 minute, allowed to fall gradually upon the preparation (beginning at 

 one aide), until it become* perfectly wetted with the balsam. The 

 Rl*M may now b* alighUy pressed in order to force out the superfluous 

 balsam, and the preparation allowed to cool. 



We uow proceed to give a few direction* for the examination of 

 particular object*, more especially animal tissues, at then of all other* 

 are the most difficult to manage. In the examination of tissues 

 containing blood-vessels, ducts, or other tubular organs, it is frequently 

 most desirable that inj<-ctions should be made before they are sub- 

 mitted to the microscope. This operation requires great delicacy. 

 A very small syringe, or small syringes according to the delicacy of 

 the structure, must be employed. The fluid injected consists of sixe 

 or gvlstine, coloured with various substances, as vermilion, aulphuret, 

 and iodide of mercury, chromate of lead, imligo, Prussian blue, white 

 lead, Ac., according to the colour wished for. 



The following general rules for injection are given by Dr. Beale : 

 Great attention should b<- paid to the cleanliness of all the instru- 

 ment* to be used in injecting. The syringe should always be kept 

 rcrupulously clean anil in good order, and the injecting-cans should 

 be carefully covered, to prevent the ingress of dust. Before com- 

 mencing the operation, plenty of warm water should be at hand ; and 

 the subject should be allowed to soak for some time in a basin of 

 hot wafer, before it is attempted to inject it, in order that it may be 

 thoroughly warmed through. The temperature of the water must 

 vary according to the degree to which the injection is required to be 

 heated : if size and vermilion be used, the water need only be warm ; 

 but if melted wax be employed, the water must be so hot that the 

 band can scarcely be borne on it The length of time which the 

 preparation is allowed to soak must depend upon its bulk ; and the 

 water should be changed as soon as it becomes at all cool. With 

 to the length of time after death that is more favourable for 

 this operation, no absolute rules can be given. Generally, it may be 

 remarked that we should not attempt to inject while the rigor mortii 

 lasts. Many days may in 'some cases with advantage be allowed to 

 elapse, particularly if the weather is cold, while in warm weather we 

 are compelled to inject soon after death. As a general rule, the more 

 delicate the tissue, and the thinner the vessels, the sooner should the 

 injection be performed. Many of the lower animals, annelids, mol- 

 lusca, Ac., and fishes, should be injected soon after death. In making 

 minute injections of the brain, only a short time should be allowed 

 to elapse after the death of the animal, before the injection is com- 

 menced. Injections of the alimentary canal of the higher animals 

 should be performed early not more than a day or two after death. 



When the preparation is warmed through, the injection properly 

 atniiued, and the pipe fixed in the vessel, we may proceed carefully 

 to inject, taking care that the injection is kept at a proper tempera- 

 tun-, by allowing it to remain in the warm water-bath during the 

 operation. 



The air should be first withdrawn from the upper part of the Teasel 

 by means of the syringe, after which the stop-cock is turned off and left 

 attached to the pipe. The syringe is then disconnected, and after being 

 washed out once or twice with warm water, is nearly filled with injection, 

 which must be well stirred up immediately before it u taken. The 

 syringe should not be quite filled, in order that the air in the pipe 

 may be made to rise into the syringe through the injection, by the 

 ascent of the piston, before any of the latter is forced into the vessel. 

 The end of the syringe is then to be pressed firmly into the upper 

 part of the stop-cock, with a slightly screwing movement. 



The piston is now very gently forced down by the thumb until the 

 syringe has been nearly empti. d, when the stop-cock must be turned 

 oil, and the syringe refilled with warm injection at before. 



Care must always be taken to keep the syringe in an inclined 



in, so that any air which may be in it may remain in the upper 



part ; and, for the same reason, all the injection should not be forced 



out, for fear of the inclosed air entering the vessels, in which case all 



chance of obtaining a successful injection would be destroyed. 



After a certain quantity of fluid has been injected, it will be neces- 

 sary to use a greater amount of force, which, however, must be 

 increased very gradually, and should only be sufficient to depress the 

 piston very slowly. If too great force be employed, extravasation will 

 bo produced before the capillaries are half filled. Qentle and very 

 gradually increased pressure, kept up for a considerable time, will 

 cause the minute vessel* to become slowly distended without giving 

 way to any great extent At th same time it must be borne in mind 

 that extravasation frequently occurs at various points in a successful 

 injoction ; but the longer this event can be kept off, the more likely 

 are we to succeed. 



In order to examine the structure of many tissues, it is necessary 

 to obtain a section sufficiently thin to permit the transmission of the 

 light readily, and so evenly cut, that the minute structure of the 

 tisuc may be submitted to exainin itiou in every part of the section. 

 The difficulty of making thin sections of many textures is often very 

 groat, and, to effo t this object satisfactorily, a knowledge of certain 

 mechanical operations becomes nec.-asary. .Sometimes we require to 

 cut a thin section of a soft pulpy texture, which can scarcely be 

 lunched without injuring its delicate structure, and altering the posi- 



tion of iU constituents ; while, in other instance*, we must obtain a 

 very thin transparent section of a substance so hard that steel tools 

 will scarcely scratch it, such as the enamel of teeth, fossil teeth, Ac. 



Previous to the examination of a tissue, boiling is frequently of 

 nn ;.. 



For instance, the fibres of which tho crystalline lens is composed 

 are best shown after boiling the lens in water. The branched muscular 

 fibres in the tongue of the frog, and in other situations may be made 

 out very readily by boiling the organ in water for a few momenta, and 

 then tearing up small portions with fine needles. Beautiful sections 

 of muscular fibre can often be obtained after the texture has been 

 boiled in water. Various glands and other texture* often require to 

 be boiled some time in water,' in order to harden them sufficiently to 

 enable us to cut thin sections; but in all cases the microscopical 

 characters of the recent texture should be examined, as well as that 

 which has been hardened by boiling. Small portions of tissue can be 

 readily boiled in a teat-tube over the spirit-lamp. 



Not uufrequeutly we wish to get rid of the soft and more pulpy 

 part of a tissue, in order to subject the more dense and fibrous portion 

 to examination. This object is usually effected by soaking the tissue 

 in water for some little time, and then placing it under a running 

 stream of water, by which means the softer portions are gradually 

 washed away. Soaking in water frequently enables us to tear up a 

 tissue very readily with the aid of needles, and thus to demonstrate 

 its structure. Occasionally it is found necessary to press the tissue, and 

 rub parts of it together, before the soft pulpy portions can begot rid of. 

 In this way we may demonstrate the supporting or trabecular tissue 

 of the spleen, and the areolar and vascular tissue of the liver, &c. 

 Thin sections of kidney, liver, and other glandular organs, may be thus 

 treated when the matrix is to be subjected to examination separately. 



Thin sections of various tissues can frequently be obtained only by 

 first drying the substance thoroughly, and then cutting off a thin 

 shaving with a sharp knife. In thin way specimens of skin, mucous 

 membrane, and many other tissues, are often most advantageously 

 prepared. The tissue is stretched on a board with pins and then 

 allowed to dry, when a very thin section can be cut off and examined 

 in Canada balsam; or it may be placed in water for a short time, in 

 which case, when subject to examination, it will often be fouud to 

 have regained its first appearance. Portions of muscular fibre, the 

 tongue, skin, and many other tissues, may be allowed to dry in this 

 manner, and then we may with a sharp knife readily obtain exceed- 

 ingly thin sections, which could not be procured in any other manner. 

 The drying may be effected in a warm room, or iu a current of air. A 

 high degree of artificial heat should be avoided. 



When the inorganic portion of a tissue which we wish to examine 

 is not altered by exposure to a red-heat, recourse may be had to 

 ignition, in order to got rid of the animal matter. In this way crystals 

 of carbonate and phosphate of lime, and granules of siliceous matter, 

 may be separated from the organic material with which they were 

 combined. The beautiful siliceous shells of the Dlatomactac may be 

 separated from organic matter by a similar process. The ignition 

 should be performed in a small platinum capsule, or upon a small 

 piece of platinum foil. The carbonaceous residue must be exposed to 

 the dull red-heat of a spirit-lamp for some time, until only a pure 

 white ash remains, which will be found to contain the objects of our 

 search in a very perfect state. If the siliceous matter only is wanted, 

 the ash should be treated with strong nitric acid, which will dissolve 

 any carbonate or phosphate. The insoluble residue may then be 

 washed and dried, and subjected to microscopic examination while 

 immersed in turpentine or Canada balsam. In many cases this method 

 is superior to that of boiling in nitric acid in order to remove the 

 organic matter. Both processes may however be employed where 

 only the siliceous residue is wanted, but if we require the salts of lime 

 ignition at a dull red-heat is alone applicable. 



In order to subject a portion of tissue or other substance to exa- 

 mination by transmitted light, the following plan is adopted : One 

 of the glass slides is carefully cleaned, and the thin section of tissue 

 which has been removed by the aid of forceps and scissors, or a scalpel, 

 placed in the centre ; a drop of clean water is then added, and the 

 whole covered with a square of thin glass, also perfectly clean. If 

 the under surface of the thin glass be gently breathed upon it becomes 

 wetted more easily. The substance may be unravelled with needles, 

 or, if necessary, any other operation performed before covering it with 

 the thin glass. If the substance bo covered with too much soft pulpy 

 matter, it may be slightly washed in water before being placed upon 

 the slide, or a jet of water from the wash-bottle may be forced upon 

 it. Thin sections will require to be laid flat upon the slide, with 

 the assistance of needles and forceps. 



Hard tissues require a different treatment Here the great object 

 is to make sections thin enough for tho object to be seen by trans- 

 mitted light 



Many hard substances, such as nail, born, and dried animal textures, 

 way be cut with a strong sharp knife, or with a razor; on operation 

 which in easily performed by placing the substance upon a piece of 

 soft deal board, and, after cutting a smooth edge, removing a thin 

 shaving, which may be examined dry or in fluid, or may bo placed in 

 Canada balsam, as occasion may require. 



Such substances as bone, ivory, and fossilised rocks, should be first 



