817 



MICROSCOPE, USES OF TH?. 



MICROSCOPE, USES OF THE. 



81S 



of air, which becomes accumulated in the hairy parts of plants, in the 

 intercellular canals, in the vessels, and in wood ; it is best removed by 

 placing the object for a few minutes in a small watch-glass filled with 

 alcohol ; when taken out of the alcohol it must be put into water, and 

 then transferred to the slide. When it ia wished to examine the cell 

 contents, in which the changes are generally produced by the operation 

 of alcohol, the removal of the air may be advantageously effected by 

 the use of the compreasorium, which is permitted to operate conti- 

 nuously upon the object, whilst the observer looks into the microscope. 

 In the absence of a compressorium, the fingers may be lightly pressed 

 against the glass cover. 



For transferring objects from one fluid into another a very fine 

 camel's-hair brush should be employed ; needles and other sharp 

 instruments should never be used for this purpose, since the object 

 may be easily injured by them. When the object is very small it 

 will be more easily found if the watch glass is placed upon a dark 

 back-ground. 



The microscope only affords a view of one surface of an object ; 

 when, therefore, bodies are subjected to examination, it is not sufficient 

 for a correct understanding of them to examine one side only; a 

 transverse section and a longitudinal section, and, in fact, frequently 

 many longitudinal sections in different determinate directions, must 

 be carefully examined and compared with one another before the 

 observer can be satisfied that he haa made out the construction of the 

 body under observation. That which in objects of large size is 

 attained by the help of the knife, is effected, in the case of very 

 small opaque. objects, by examining them on different sides. In 

 examining small bodies which are very transparent, as, for instance, 

 the ovules of Orchidere, or grains of pollen or starch, the adjustment 

 of the miscroscope is varied from time to time, by which means the 

 upper side of the object is first brought into the focus, then the 

 middle (which may be called an optical section, transverse or longitu- 

 dinal, as the case may be), and, lastly, the under-side. The more 

 perfect the object-glass the more exact is the focal plane, and the more 

 sensitive is the instrument to any small alteration of the focus, on 

 which account the observer should always keep his hand upon the 

 fine-adjusted screw whilst he is employed upon observations requiring 

 much accuracy. The sensitiveness above mentioned increases, iu 

 good instruments, in proportion to the magnifying power, and also 

 with the angle of the aperture of the glass. 



The accurate adjustment of an object is judged of by the sharpness 

 of delineation of the image. The adjustment is more accurate in pro- 

 portion to the delicacy and sharpness of the lines seen upon small 

 objects, and also in proportion to the fineness and clearness of the 

 outline, which should be soft, but well-defined. The scales of the 

 Jfipparchia, Janira, a common brown Butterfly, are well adapted 

 for enabling a person to judge of the accuracy of an adjustment; the 

 smallest change of focus causes transverse striae to disappear. 



In examining small round bodies, such as pollen-grains, the position 

 of the object* should be changed, by gently pushing the glass-cover so 

 as to cause the bodies to roll about ; by this means different sides of 

 the objects are >een, and from the different images presented to the 

 eye their true form is made out. 



Small objects should never be compressed between two glass sides, 

 that being too rough a method of proceeding. If however it is supposed 

 that anything is to be gained by compression, then it is advisable to use 

 the compressorium, which is an instrument consisting of a mechanical 

 arrangement by which the thin glass covering an object may be com- 

 pressed at will. When the compressorium is cautiously used, the 

 observer, by carefully watching what takes place, can gain a knowledge 

 of the changes produced by pressure during the time the compressorium 

 is permitted to work. In certain cases, where, for instance, the question 

 is whether a particular object is a delicate cell or a drop of some 

 fluid, the Compressorium may be of service ; since, if a cellular mem- 

 brane be present, it will burst and discharge its contents as the pressure 

 w increased, whereas the drop, whether it bo oil, liquid resin, or any 

 other chemical substance upon the slide, will only change its form. 



In examining any object, whether animal or vegetable, it is not 

 sufficient to observe the nature, form, and arrangement of the cells ; 

 it is necessary also to pay attention to their contents, which, in the 

 case of plants, are different according to the functions assigned to 

 them by nature. It is necessary, therefore, to distinguish 1st, 

 Whether a cell is empty, that is to say, whether it contains air, as is 

 the case, for instance, with perfect vessels and wood-cells; 2ndly, 

 Whether its contents are fluid with a solid substance contained in the 

 fluid. Another question which arises is as to the nature of the fluid 

 contents, that is, whether they consist of a homogeneous fluid, or of 

 fluirls of different consistencies, apparently not intermingling with one 

 another ; the manner in which these fluids are affected by chemical 

 re-agents ban also to be considered. Lastly, the solid ingredients of 

 the cell-contenta, and their physical and chemical nature, must also be 

 attended to. There are some substances dissolved in the juices of the 

 cell, such as sugar, for example, for which no certain chemical re-agents 

 are known. Gum and dextrine are coagulated by alcohol ; the presence 

 of nitrogenous substances is proved, by the use of sugar and sulphuric 

 acid, which produce a red colour, or by a solution of iodine, or of 

 chlorfde of zinc and iodine, and also by nitric acid, with ammonia 

 subsequently added to it; in these three cases an intense yellow 



AT. HIliT. KIT. VOL. III. 



colour, almost brown, is produced. When the presence of oil or resin 

 is suspected, the object should be placed in ether or pure alcohol for 

 some hours, which will dissolve both oil and reain. When the juices 

 of the cell hold any salt in solution, some re-agent must be used 

 which operates upon the salt. Starch is detected by being coloured 

 blue by iodine. [STARCH ; LIGNIN ; CHLOROPHYLE ; PROTEIN.] 



The following is a list of re-agents which it will be found convenient 

 to have close at hand iu the examination of either animal or vegetable 

 substances : 



1. Alcohol, which is used principally for removing air from sections 

 of wood and other preparations, and aa a means of dissolving certain 

 colouring matters, &c. It coagulates the albuminous textures of 

 animals. 



2. Ether, which is principally used for dissolving resins, fatty essential 

 matters, and other oils, &e. This is also useful for removing air. 



3. A solution of caustic potash, which is used for the purpose of 

 dissolving fat, is also useful in certain cases from its effects upon tho 

 contents of cells, and upon the thickening layers. It dissolves up 

 substances of an albuminous nature. This solution often works better 

 after warming. 



4. A solution of iodine (one grain of iodine, three grains of iodide 

 of potassium, one ounce of 'distilled water) for colouring the cell- 

 membrane, and the contents of the cell. 



5. Concentrated sulphuric aci<J. This is principally used for 

 examining pollen and spores. In the examination of hairs it renders 

 the cells very distinct. 



6. Diluted sulphuric acid (three parts of sulphuric acid and one 

 part water), for colouring the cells of plants which have been pre- 

 viously moistened with the solution of iodine. The object is 

 moistened with the solution of iodine, which is then removed with 

 a fine camel's-hair brush, and by means of a glass rod a drop of 

 sulphuric acid is added, and the object is then immediately covered 

 with a covering-glass. The effect of the sulphuric acid and iodine, as 

 well as that of the iodised solution of chloride of zinc, is not always 

 the same over the whole surface of an object. At the points where 

 the mixture is more concentrated, the colouring is more intense ; 

 frequently places remain without any colour. The colour changes after 

 some time ; iu twenty-four hours the blue is often changed into red. 



The iodised solution of chloride of zinc produces generally the 

 same blue colour in cellulose as iodine and sulphuric acid : the former 

 is preferable iu many cases, inasmuch as its effect is not so rapid, and 

 it is not injurious to the cells. Both re-agents should in many cases 

 be employed, and their effects compared with one another. Besides 

 maceration, it is advisable, in examining woods, to adopt the plan of 

 boiling thin sections for about a minute with a solution of caustic 

 potash ; after this boiling, the wood-cells, which were not previously 

 turned blue by iodine and sulphuric acid, become of a violet or blue 

 colour upon the application of the iodised solution of chloride of zinc. 



7. A solution of chloride of zinc, iodine, and iodide of potassium. 

 A drop of this solution applied to an object placed in a little water, 

 produces the same colour as iodine and sulphuric acid. This solution 

 was first recommended by Professor Schultz, of Rostock ; it is more 

 convenient to use than iodine and sulphuric acid, and produces almost 

 the same results ; it is, moreover, not so destructive as sulphuric acid. 

 The exact prescription for this solution is as follows : Zinc is dissolved 

 iu hydrochloric acid ; the solution is permitted to evaporate, under 

 contact with metallic zinc, until it attains the thickness of a syrup ; 

 and the syrup is then saturated with iodide of potassium. The 

 iodine is then added, and the solution, when it is necessary, is diluted 

 with water. 



8. Nitric acid, or, what is better, chlorate of potash and nitric acid. 

 This is used for separating cells. The method of maceration dis- 

 covered by Professor Schultz, and which is much to be recommended, 

 is as follows : The object (wood, for instance), is reduced in size to 

 the thickness of a lucifer-match ; it ia then thrown into a long and 

 tolerably-wide boiling-tube ; to this is added, iu a little while, an 

 equal volume of chlorate of potash, and as much nitric acid as is at 

 least sufficient to cover the wood and the potash ; the tube is then 

 warmed over a spirit-lamp; a brisk development of gas quickly 

 appears ; the boiling-tube is withdrawn from the flame, the oxydising 

 mixture is permitted to work for about a minute and a half or three 

 minutes, and the whole is thrown into a saucer with water : the small 

 pieces which adhere slightly to one another are then collected, placed 

 in the boiling-tube, and boiled repeatedly with alcohol, until the latter 

 appears colourless ; they are then boiled once more, for the last time, 

 with water. By the help of the simple microscope the cells ara now 

 separated from one another with a needle, and selected. The boiling 

 with nitric acid and chlorate of potash should never be carried on iu 

 the room where the microscope is kept, because its glasses might be 

 injured by the evaporation which is developed. Thin sections of 

 plants, for instance, of woods or leaves, are warmed for half a minute, 

 or a minute, in a watch-glass ; the boiling is unnecessary in this case ; 

 the section is taken out with a little rod, and thrown into a small 

 watch-glass, with water. Nitric acid is one of the best agents for 

 removing animal or vegetable tissues from silica, as iu the case of tho 

 Diatomacece. 



9. Oil of lemons, or any other essential oil, for examining pollen 

 and spores. 



3 u 



