tion is carefully examined with a first-class objective of sufficient amplification, it will be found that they have not run into each other, but that, on the contrary, the outlines of almost every individual may be discerned, however distorted they may be. As in this experiment the blood-corpuscles are pressed completely flat, they represent minute plates with level surfaces, through which the rays of light pass without undergoing much or any refraction, except in places where a difference in the properties of their substance might exist. But, as the membraneous layer is probably somewhat differentiated from the rest of the body, it is seen at the margin of the blood-corpuscle in the form of a light greenish border. By applying a drop of water to the preparation before it has become dry, the blood - corpuscles are gradually rendered pale and faint; and their greenish borders will now appear in the form of distinct delicate double contours, as described before. In proportion to the amount of pressure previously sus tained, they will retain their dimensions and their flatness; and in those places where they were crowded before the application of pressure, whether mutual or by the covering glass, and in consequence much distorted in shape, they will be seen separating from each other as the water takes effect, and floating away, presenting the same appearances as the others described. In the course of my investigations into the structure of the coloured blood-corpuscles of Man, I also studied the effect of various reagents, such as chloroform, acetic, nitric, and carbolic acids, alcohol, as well as solutions of hydrate of chloral, boracic and chromic acids, &c., either in the gaseous or liquid form, upon these bodies. The changes observed to take place on these corpuscles by the action of these agents are, though not in every instance exactly alike, yet similar to those we have seen to occur on the blood-corpuscles of the Amphiuma or the Frog; they mainly consist in the escape or destruction of the hæmoglobin, contraction or coagulation of the protoplasm, change of form, &c. As I have described them before in connection with the bloodcorpuscles of these Amphibia, they require no further remarks for our special purpose, except that they all appear to corroborate my view of the simplicity of the structure of the non-nucleated coloured blood-corpuscle, as well as of that of the nucleated. In concluding this treatise on the structure of the coloured blood-corpuscles, I have only to add that I still believe a part of their function to be secretory. In accordance with this view I regard them as true glandular cells, which, independent of the part they may act in the transfer of ozone, are also engaged in appropriating certain materials from the plasma of the blood, in order to transform them into other bodies by virtue of their secretory power, and to finally return them to that fluid in the special condition required for the subservience of other purposes, such as the preservation of the normal constitution of the blood, as well as the nutrition of the various tissues. Changes in the substance and form of the coloured bloodcorpuscles of Man, similar to those above described, and which may be detected by the aid of the microscope, occur in various pathological conditions of the system. Although some attempts have been made by several pathologists to study these changes, no definite results have to my knowledge hitherto been obtained. The cause of this seeming failure, however, evidently depends on the difficulty attending the investigation of this subject, and I entertain no doubt as to the final success of these studies, if conscientiously and steadily pursued. For a number of years I have occasionally directed my attention to this subject, and have become convinced that changes in the form and character of the coloured bloodcorpuscles of Man, which may be detected by microscopical examination, do occur in pathological states of the system; but as my observations were confined to only a few diseases, as yellow fever and rheumatism, and were not made systematically, I shall forbear entering upon this subject at present. After I shall have accumulated additional facts to those already obtained, and on a more extended scale, I hope to present them in proper form to the profession. II.-On the Present Condition of Microscopy in England. (Read before the ROYAL MICROSCOPICAL SOCIETY, April 3, 1878.) My object this evening (writing throughout in the spirit of the Publican and not of the Pharisee) is to call attention to what I think is an indisputable fact, that in recent years no substantial progress has been made in this country either in the knowledge of the theoretical principles of the microscope itself, or in the systematic investigation of microscopical phenomena. The microscope has, in fact, come to be regarded merely as the tool of the naturalist and the histologist; and notwithstanding the objects for which this Society was established, it may, I think, be truly said that out of the entire scientific world there is probably no body of men who devote so little real attention to the principles that lie at the root of that branch of science of which they are disciples, as do the English microscopists. As a particular instance, I may refer to the apathy that has been shown in regard to the researches of Professor Abbe on the theory of the microscope, researches undoubtedly as important as any that can be found in the whole of its history, and rivalling even the discovery of achromatism, or that of Lister on aplanatic foci. It is, I think, not a little humiliating that such a discovery -in one aspect so simple-should not have originated in this country, we being the first, and for many years the only, nation to maintain a "Microscopical" Society. Whatever may be the cause of such apathy, it is evident that it cannot be attributed to any deficiency in the power of perseverance; for when we enter upon the discussion of a question, say of angular aperture, we do not rest content until a point has been reached which renders it impossible for anyone to say that the subject has not been exhausted to the very last limits. For this the condition of our literature is in part answerable. Recall the contents of the generality of modern English treatises on the microscope, and what do we find? Out of a given number of pages, a very small portion only is devoted to the optical prin * The statement of the "Objects of the Society," prefixed to the Charter and Bye-laws, sets forth that "the Society was established for the promotion and diffusion of improvements in the optical and mechanical construction, and in the mode of application, of the microscope: "For the communication and discussion of observations and discoveries tending to such improvements or relating to subjects of microscopical observation : "For the exhibition of new or interesting microscopical objects and preparations, and for the formation of an arranged collection of such objects: "For affording the opportunity and means of submitting difficult and obscure microscopical phenomena to the test of instruments of different powers and constructions:“For the establishment of a library of standard microscopical works.” ciples of the microscope and to microscopical phenomena (about as much as is to be found prefaced to foreign books on histology or botany that do not pretend to be treatises "on the microscope" at all), and what is given is in the most elementary form that can be conceived. The remainder of the book is avowedly a condensed summary of the whole range of subjects belonging to natural history-a small natural history cyclopædia.* If we compare our books with those of some other countries, in particular Germany and Holland, the conviction must be forced upon us that we in England have not in modern times kept pace with the progress that has been made elsewhere. I am not venturing to reflect in any way upon our authors, the blame must rest upon ourselves and not upon them. The supply is necessarily regulated by the demand-if there is no demand there can hardly be expected to be any supply, so that any improvement must originate from ourselves. The principal reasons, as I conceive, for this state of things are these. In the first place, a feeling has gained ground amongst us that the only proper field for the microscopist is to be found in the investigation of one or other of the many branches of natural science that require the aid of the microscope, and hence the theory of the microscope itself and of microscopical phenomena is regarded as altogether puerile and unworthy of the attention of the true microscopist. For myself, I may freely confess that (erring, no doubt, in the opposite extreme) I take a comparatively small interest in the subjects to which the microscope is applied, and that I am almost inclined to look on the term "microscopist" as not being properly applicable to those who are engaged in the study of natural history, even although it may be essentially by means of the microscope-in fact, that as it has been said "the proper study of mankind is man," so the proper study of the microscopist is the microscope. It has been objected, and no doubt will be objected again, to this view, that it is fallacious, in so far as it exalts to an end that which ought only to be looked upon as the means to the end—that the microscope (as I was recently told) can be properly regarded as nothing more than the ladder by which we climb to a point from which a better prospect may be obtained, and that it is a waste of time in such a case to devote attention to the ladder rather than to the prospect. Such an argument-one that exalts the applications of a science at the expense of the investigation of its theoretical principles, on *This does not, of course, apply to books that do not pretend to describe the microscope, but to furnish directions for its use. the ground of the greater practical value of the one over the. other-is a strange one to be used by scientific men. It is the merest truism to say that the only sure way to advance any branch of knowledge is by undertaking a complete and exhaustive investigation of the theoretical principles on which it is based. All the practical inventions ever made have depended for their discovery on the previous investigation of mere theories, by men who pursued knowledge for its own sake alone, and without stimulus from any notions of practical utility. As an old writer (Malthus) has put it :-"It surely would be most unwise to restrain inquiry conducted on just principles, even where the immediate practical utility of it is not visible. In every branch of natural philosophy how many are the inquiries necessary for their improvement and completion which, taken separately, do not appear to lead to any specifically advantageous purpose; how many useful inventions and how much valuable and improving knowledge would have been lost if a rational curiosity and a mere love of information had not generally been allowed to be a sufficient motive for the search after truth."* If only the lowest view of the microscope is to be accepted, the improvement of the mere tool must necessarily have an important influence on the perfection of the work performed by its aid, so that the improvement of the microscope will directly further the aims of the naturalist. Another reason which has also operated to produce the present condition of things is, that some kind of belief, more or less definite, has grown up, that we have arrived substantially at a state of perfection, or at the limits of the possible; that there being no further scope for improvement, the study of theoretical principles has become a matter entirely of antiquarian research. I should not have thought that such a belief could be seriously held, had it not received the sanction of one of our high living authorities, who, whilst sufficiently cautious to guard himself against being supposed to assert the absolute impossibility of further improvement, yet, after speaking of the microscope as having "acquired the deserved reputation of being one of the most perfect instruments ever devised by art for the investigation of nature," ventures to say that "the statements of theorists as to what may be accomplished are so nearly equalled by what has been effected, that little room for improvement can be considered to remain until chemists furnish opticians with new varieties of glass whose refractive and dispersive powers shall be better suited to their requirements."† * Principles of Political Economy.' This point has also been well treated by Professor Tyndall in his concluding lecture on Light. + Carpenter, 5th ed., 1875, p. 6. |