To those commencing the study of the medical profession this little, book will be found very valuable. Few of the manuals that have been published with the same object in view are so much up to the time as this little work by Dr. Bennett. We are induced to give it a notice in our pages, as out of the six lectures of which it consists two are devoted to the Microscope as a means of diagnosis. Nor do we think the space thus occupied disproportionate to the just value of this instrument in the hands of the medical practitioner. A successful treatment of disease, let practical men say what they will, can only be insured by an accurate knowledge of disease; and there can be no accurate knowledge of diseased tissues or morbid actions but by the aid of the microscope. It must not, however, be supposed that the microscope is an instrument easily used; that all a man has to do in order to profit by its revelations is to purchase an expensive apparatus at one of our great opticians. As with the eye itself, the practice of observation with the microscope demands a careful education. Only by instruction under a careful teacher or a systematic course of private observation can any one expect to use this instrument with success. Whether for public courses or private study, Dr. Bennett’s book will supply a good outline of the objects that ought to be examined by a medical man. The principal physical characters to be regarded in microscopic examinations are described in the following passages:—
“1. Shape.—Accurate observation of the shape of bodies is very necessary, as many of these are distinguished by this physical property. Thus the human blood globules, presenting a biconcave round disk, are in this respect different from the oval corpuscles of the camelidæ, of birds, reptiles, and fishes. The distinction between round and globular is very necessary to be attended to. Human blood corpuscles are round and flat, but they become globular on the addition of water. Minute structures seen under the microscope may also be likened to the shape of well-known objects, such as that of a pear, balloon, kidney, heart, etc. etc.
“ 2. Colour.—The colour of structures varies greatly, and often differs, under the microscope, from what was previously conceived regarding them. Thus the coloured corpuscles of the blood, though commonly called red, are, in point of fact, yellow. Many objects present different colours, according to the mode of illumination ; that is, as the light is reflected from or transmitted through their substance, as in the case of certain scales of insects, feathers of birds, etc. Colour is often produced, modified, or lost, by re-agents, as when iodine comes in contact with starch corpuscles, when nitric acid is added to the granules of chlorophyle, or chlorine water affects the pigment cells of the choroid, and so on.
“ 3..Edge or Border.—The edge or border may present peculiarities which are worthy of notice. Thus it may be dark and abrupt on the field of the microscope, or so fine as to be scarcely visible. It may be smooth, irregular, serrated, beaded, etc. etc.
“ 4. Size.—The size of the minute bodies, fibres, or tubes which are found in the various textures of animals can only be determined with exactitude by actual measurement in the manner formerly described. It will be observed, for the most part, that these minute structures vary in diameter, so that when their medium size cannot be determined, the variations in size from the smaller to the larger should be stated Human blood-globules in a state of health have a pretty general medium size ; and these may consequently be taken as a standard with advantage, and bodies may be described as being two, three, or more times larger than this structure.
“ 5. Transparency.—This physical property varies greatly in the ultimate elements of numerous textures. Some corpuscles are quite diaphanous, others are more or less opaque, The opacity may depend upon corrugation or irregularities on the external surface, or upon contents of different kinds. Some bodies are so opaque as to prevent the transmission of the rays of light, when they look black by transmitted light, although they be white, seen by reflected light. Others, such as fatty particles and oil globules, refract the rays of light strongly, and present a peculiar luminous appearance.
“ 6. Surface.—Many textures, especially laminated ones, present a different structure on the surface from that which exists below. If, then, in the demonstration these have not been separated, the focal point must be changed by means of the fine adjustment. In this way the capillaries in the web of the frog’s foot may be seen to be covered with an epidermic layer, and the cuticle of certain minute fungi or infusoria to possess peculiar markings. Not unfrequently the fracture of such structures enables us, on examining the broken edge, to distinguish the difference in structure between the surface and the deeper layers of the tissue under examination.
“ 7. Contents.—The contents of those structures, which consist of envelopes, as cells, or of various kinds of tubes, are very important. These may consist of included cells or nuclei, granules of different kinds, pigment matter, or crystals. Occasionally their contents present definite moving currents, as in the cells of some vegetables, or trembling rotatory molecular movements, as in the ordinary globules of saliva in the mouth.
“ 8. Effects of lie-agents.—These are most important in determining the structure and chemical composition of numerous tissues. Indeed, in the same manner that the anatomist with his knife separates the various layers of a texture he is examining, so the histologist, by the use of reagents, determines the exact nature and composition of the minute bodies that fall under his inspection. Thus water generally causes cell formations to swell out from endosmosis ; whilst syrup, gum-water, and concentrated saline solutions cause them to collapse from exosmosis. Acetic acid possesses the valuable property of dissolving coagulated albumen, and, in consequence, renders the whole class of albuminous tissues more transparent. Thus it operates on cell walls, causing them either to dissolve or become so thin as to display their contents more clearly. Ether, on the other hand, and the alkalies, operate on the fatty compounds, causing their solution and disappearance. The mineral acids dissolve most of the mineral constituents that are met with, so that in this way we are enabled to tell with tolerable certainty, at all events, the group of chemical compounds to which any particular structure may be referred.”
Short accounts are given in the book of the appearances of the saliva, milk, blood, pus, sputum, vomited matters, faeces, uterine and vaginal discharges, mucus, dropsical fluids, urine, and cutaneous eruptions and ulcers. In a manual of 130 pages, of course no detail could be expected on these subjects. What is given bears the stamp of being the result of the author’s own investigations on the subjects he treats, and will be found all the more valuable as coming from one who is a good physiologist as well as a diligent practical physician.
