The micrographic dictionary : a guide to the examination and investigation of the structure and nature of microscopic objects / by J.W. Griffith and Arthur Henfrey.

Date:
1875
Catalogue details

Licence: Public Domain Mark

Credit: The micrographic dictionary : a guide to the examination and investigation of the structure and nature of microscopic objects / by J.W. Griffith and Arthur Henfrey. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    simply as a means of vieivm;/ minute objects, and judging- of their nature from the simple inspection of them under the conditions in which they naturally or accidentally occur. Such a procedure, the most casual Gbseryer must be well awai'e, is never trusted alone in the examination of objects visible to the naked eye, being almost sure to lead to erroneous conclusions. Consider the common course pursued in the examination with the unaided sight, of a body for the first time presented to our notice ! The first point is the exami- nation of its general appearance and colour ; the relative position of the eye of the observer and the object is then changed, so that an idea of its solidit}' may be obtained; its weight is next perhaps determined by taking it in the hand ; it is presented to the light in various ways, in order to judge of its transparency, and of the optical properties of its surface. If the object be at a distance, its size is judged of by comparing its apparent size with that of adjacent bodies, whose dimensions are approximately known; and its luminousness is also taken into consideration, it being known generally that the nearer bodies of the same size are to us, the more luminous they appear. The observer then is either satisfied with the conclusions drawn from reasoning upon the results thus obtained, or he makes besides a chemical examination. Again, care should be taken to avoid forming an opinion upon the normal or abnormal state of an organic structure, without a previous knowledge of the natural structure of organic tissues. We therefore recommend the student, before he thinks of recording his observations, to begin by testing the structure of any objects which may come in his way, or that of the Tkst-objects which we have described, according to the rules laid down in the second part of this Introduction. It may be remarked for those who have but small means at their command, and who are unable to procure a first-rate English microscope, that perhaps very many of the facts elicited by the use of this instrument have been determined by our continental neigh- bours with far less perfect instruments, who have made up for the imperfections of their instruments by extreme patience, care, and repeated observation; which can be done to an extent that would scarcely have been anticipated. We have alluded to these sources of error merely for the purpose of warning future observers, and impressing upon them the importance of making themselves acquainted with the difficulties attendant upon microscopic investigations, and with the best means of overcoming them. In fact, it may be briefiy stated that the object of the present work is to guide the microsci ipist in his researches, to give him a notion of the manner of making these researches, also some account of the characters, microscopic structure, and properties of objects in general, and to show how he may most easily arrive at satisfactory results. But there are difficulties inherently connected with the examination of microscopic objects, which are not encountered when objects are examined with the naked eye. One of these is that, with the ordinary microscope, objects are only viewed with one eye; hence we lose the direct power of distinguishing solidity, &c., and are compelled to resort to indirect means for these purposes. This difficulty is to some extent overcome by the con- struction of binocular microscopes. Again, the ordinary objects around us are also usually viewed by reflected light, whilst with the microscope they are mostly viewed by trans- mitted light, and we are consequently much less practised in judging from the appearances of objects thus illuminated, and are therefore liable to err. Another, but a less important difficulty in microscopic investigations, or at least mani- pulations, consists in the image of tlie objects being inverted. Erecting eyepieces, as they are called, will obviate this difficulty; but as they are expensive, and interfere with the distinctness of the images of the objects, and as the difficulty is to a great extent got over by practice, they are rarely used.