11 



MIC'ROPUS. 



MICROSCOPE, USES OF THE. 



811 



Moltiuca, it the food of the Steamer-Duck* St. Iracltyptenu, and if. 



(' Narrative of the Surveying Voyages of H.M.S. Adventure and 



icropttnu comet very near to tfieropttra, Qravenhorst'a name for 

 a genua of Coleopterous Insects, and to Microptere of Laccpode, who 

 OMB the term to designate a genus of Acanthopterygious Fishes. 



MTCROPUS (Swainson), a genus of Birds belonging to the family 

 Brachypotlincr, the first sub-family of the Ueruiida, according to his 

 arrangement. [McBULUXO.] 



M. ckaicocepkalut ; Ixot chalcocqihaliu, Temm. The male has the 

 whole head covered with a sort of hood of metallic black with violet 

 reflections ; the neck, the shoulders, the back, and wings, dull gray or 

 lead colour ; breast deep gray, which becomes brighter on the other 

 lower parts of the body; wings black, but the secondaries gray, 

 bordered with whitish on the exterior barbs ; tail gray, with a trans- 

 Terse black band, and terminated with a broad white border. Length 

 6 inches 4 lines. Female : less lively in colour. 



It inhabits Java, where Van Hasselt found it in the wild and woody 

 district of Bantam. 



* 



Micropus chalcocfphalu* (male). 



MICROSCOPE, USES OF THE. There are few instruments that 

 have rendered such important aid in scientific search as the Microscope. 

 The chief advances that have been made in the natural history sciences, 

 embracing physiology, during the latter portion of the first half of 

 the lyth century, have been effected by its agency. The structure of 

 this instrument has been gradually rendered more perfect as the 

 science of optics advanced ; and its nature and arrangement can only 

 be understood by the study of the principles of this science. In the 

 articles LIGHT, LENS, ACHROMATIC ABERRATION, MICROMETER, and 

 MICROSCOPE, in the ARTS AND SCIENCES DIVISION of this work, the 

 student will find the principles and plan on which this instrument is 

 constructed fully elucidated. We purpose here referring to its use as 

 an instrument of natural history and physiological research, and of 

 those general arrangements and applications by which its utility can 

 alone be fully secured. It is not alone sufficient that a man possesses 

 eyes in order to observe accurately, nor is it the possession of a costly 

 microscope that will enable a person to confirm the observations of 

 others or make discoveries of his own. The use of the microscope by 

 uninstructed and incautious observers has given rise to many absurd 

 errors. " The fruit of the mulberry has been mistaken for Entozoa ; 

 calcareous corpuscles have been regarded by several observers as ova, 

 and the appearance arising from the presence of concentric lamina 

 has been interpreted to be the coils of an inclosed embryo ; similar 

 corpuscles hare also been regarded as nucleated cells, and again as 

 blood-corpuscles ; minute fossils in chalk have been strung together 

 with portions of vegetable tissue, and (perhaps) the spores of Alga, 

 to constitute different stages of a fungus : minute hairs projecting on 

 the surface of a membrane have been declared to be spiculeo within 

 subjacent cells ; and quite recently one writer states, that certain 

 minute bodies which he has examined are either blood-corpuscles or 

 the spores of fungi, but which is doubtful ! while another recounts, 

 bow by fortunate accident he discovered that corpuscles, which he 

 had regarded at first as consisting of fat, were afterwards found 

 accidentally to consist of calcareous salts ! 



" Again, we read in physiological works of the yolk-cells, and the 

 coloured oil-globules of the yolk ; and a beautiful function of assimila- 

 tion has been attributed to them; but they exist only in the 

 imagination of the authors, who have regarded the one as cells, simply 

 because they are round, and the other as consisting of fat, because 

 they are highly refractive. Sit co the publication of Schleiden's cell- 

 doctrine, almost everything i uund bus been regarded as a cell ; any 

 single body within this, or where there are several, the largest has 



been regarded as a nucleus, and any spot within the nucleus has 

 been viewed as a nucleolus. Whereas many of the so-called cells are 

 homogeneous spheres, many of the nuelei are vaouoles, and a true 

 nucleolus is very rarely found except in books." (' Micrographics 

 Dictionary.') 



Against such errors as these a long-continued and careful use of the 

 microscope can alone preserve the young observer. They are not the 

 result of imperfect or inferior instruments, but the consequences of 

 hasty and imperfect observation. They have been made by persons 

 using the most costly instruments and their erroneousness demon- 

 strated by those who have used the simplest and most economical 

 arrangements. 



In microscopic observations two things must be remembered 1st, 

 That in the microscope, especially with high powers, we see surfaces, 

 not bodies. It frequently happens that in looking upon surfaces, we 

 get a glance into the depths of transparent objects by changing the 

 adjustment, without altering the position of the object; it more often 

 happens however that in looking upon such objects, we are unable to 

 make them out to be bodies until we have changed their position, and 

 ascertained their dimensions in three different directions; this, in 

 many cases, from the nature of the object itself, is a matter of great 

 difficulty. 2nd, That we seldom see the objects under the microscope 

 in their natural condition ; that we consequently must take into con- 

 sideration the changes which we ourselves partly produce, either by 

 the medium in which the object is placed, or by the use of the knife 

 or other influences. Long and thorough practice with the microscope 

 secures the observer from deceptions which arise, not from any fault 

 in the instrument, but from a want of acquaintance with the micros- 

 cope, and from a forgetfulness of the wide difference between common 

 vision and vision through a microscope. Deceptions also arise from a 

 neglect to distinguish between the natural appearance of the object 

 under observation, and that which it assumes under the microscope. 



To these difficulties must be added those originating in the eye 

 itself, through the so-called ' Mouches volantes,' and those also which 

 arise from the observer being unacquainted with the appearance, under 

 the microscope, of the common things which are dispersed through- 

 out the air and water, such as small particles of dust, &c. Lastly, 

 deceptions are also caused by air-bubbles, by molecular motion, and 

 by the currents which arise upon the stage of the microscope from 

 the evaporation of water, or from the intermingling of two fluids. 

 The observer must learn to know and distinguish all these things 

 thoroughly, and then no further deception can arise from these causes. 



The proper use of the microscope is always the principal thing to 

 be considered. Hedwig with the microscope of his time, promoted 

 the advancement of science to a greater extent than many observers 

 with incomparably better instruments have done. 



In order to use the microscope properly, the observer must be 

 skilful in handling the instrument and the objects, and above all 

 things, his mode of proceeding must be conducted with accuracy and 

 judgment, and he must be able to give a sufficient reason for every 

 thing that he does. His progress hi research will be slow, but sure ; 

 he must endeavour to obtain objects from every possible source, and 

 must examine them thoroughly ; he must verify his own observations 

 as scrupulously as possible, and so, progressing step by step, he will 

 attain the desired end. Work without method will seldom lead to 

 any result ; the finest sections of wood made only in one direction, or 

 in a wrong direction, do not lead to any knowledge of the wood under 

 observation. Single observations (of wood, for instance), irregularly 

 made from time to time, only show the condition of the wood at the 

 time of that particular observation, and throw no light on its condition 

 at an earlier or later period ; whilst sections made in a proper manner, 

 and well-preserved specimens of the successive conditions of the wood, 

 furnish irrefragable proofs, the one of the construction, and the other 

 of the development in the growth of the wood under observation. 

 (Schaoht on the ' Microscope. ) 



Before speaking of the methods of examining and preserving bodies 

 for microscopic observation, it will be better to draw attention to the 

 natural objects, to the examination of hich it bos been applied with 

 so much success. In both the inorganic and organic worlds the micro- 

 scope is made subservient to observation. To speak first of inorganic 

 substances and materials not under the influence of vital action, it 

 has been found of great use in determining the forms of minute 

 crystals. In this way it aids the analytical chemist. In the exami- 

 nation of the saline contents of water, if a small quantity of the 

 water is allowed to evaporate upon an ordinary gloss slide, its contents 

 may be judged of by the forms which the crystalline matters assume. 

 In fluids obtained from organic bodies this plan of examination has 

 been lately applied with the most interesting results. A series of the 

 most beautiful illustrations of the microscopic characters exhibited by 

 crystals obtained by the evaporation of the blood and other fluids, 

 will be found in Dr. Otto Funke'a ' Atlas [of Physiological Chemistry,' 

 and also in the ' Micrographic Dictionary,' by Dr. Griffiths and 

 Mr. Honfrey. Not only are the natural crystalline constituents 

 dissolved up in liquids thus obtained, but new combinations obtained 

 by the addition of re-agents. This mode of inquiry is equally 

 applicable to the excretions of the human body, and is rapidly 

 becoming one of the most important means of diagnosis in the hands 

 of the physician. 



