September 6, 1900] 



NA TURE 



44' 



cent 



m 



liscretion and careful prevision are as necessary in the direction 

 t public affairs as in the pursuit of science, and in both 

 instances, when properly exercised, they enable us to reach with 

 com^iaralive certainty the goal which we strive to attain. 



Improvements in Means of Observation. 



Whilst certain principles of research are common to all the 



ciences, each great division requires for its investigation 



necialised arrangements to insure its progress. Nothing con- 



ributes so much to the advancement or knowledge as improve- 



nents in the means of observation, either by the discovery of 



new adjuncts to research, or by a fresh adaptation of old 



lethods. In the industrial arts, the introduction of a new kind 



f raw material, the recogni;ion that a mixture or blending is 



often more serviceable than when the substances employed are 



uncombined, the discovery of new processes of treating the 



articles used in manufactures, the invention of improved 



machinery, all lead to the expansion of trade, to the occupation 



f the people, and to the development of great industrial 



centres. In science, also, the invention and employment of 



and more precise instruments and appliances enable us to 



reciate more clearly the signification offacts and phenomena 



ich were previously obscure, and to penetrate more deeply 



o the mysteries of nature. They mark fresh departures in 



! history of science, and provide a firm base of support from 



ich a continuous advance may be made and fresh conceptions 



of nature can be evolved. 



It is not my intention, even had I possessed the requisite 

 knowledge, to undertake so arduous a task as to review the 

 progress which has recently been made in the great body of 

 sciences which lie within the domain of the British Association. 

 As my occupation in life has required me to give attention to 

 the science which deals with the structure and organisation of 

 the bodies of man and animals — a science which either includes 

 within its scope or has intimate and widespread relations to 

 comparative anatomy, embryology, morphology, zoology, physi- 

 ology and anthropology — I shall limit myself to the attempt 

 to bring before you some of the more important observations 

 and conclusions which have a bearing on the present position 

 of the subject. As this is the closing year of the century it 

 will not, I think, be out of place to refer to the changes which 

 a hundred years have brought about in our fundamental con- 

 ceptions of the structure of animals. In science, as in business, 

 it is well from time to time to take stock of what we have 

 been doing, so that we may realise where we stand and 

 ascertain the balance to our credit in the scientific ledger. 



So far back as the time of the ancient Greeks it was known 

 that the human body and those of the more highly organised 

 animals were not homogeneous, but were built up of parts, the 

 partes dissiviilares (to av6iJ.oia ixtpij) of Aristotle, which differed 

 from each other in form, colour, texture, consistency and 

 properties. These parts were familiarly known as the bones, 

 muscles, sinews, blood-vessels, glands, brain, nerves and so on. 

 As the centuriesj rolled on, and as observers and observations 

 multiplied, a more and more precise knowledge of these parts 

 throughout the Animal Kingdom was obtained, and various 

 attempts were made to classify animals in accordance with their 

 forms and structure. During the concluding years of the last 

 ceiitury and the earlier part of the present, the Hunters, 

 William and John, in our country, the Meckels in Germany, 

 Cuvier and St. Milaire in France, gave an enormous impetus to 

 anatomical studies, and contributed largely to our knowledge of 

 the construction of the bodies of animals. But whilst by these 

 and other observers the most salient and, if I may use the expres- 

 sion, the grosser characters of animal organisation had been recog- 

 nised, little wasknown of the more intimate structure or texture of 

 the parts. So far as could be determined by the unassisted vision, 

 and so mach as could be recognised by the use of a simple 

 lens, had indeed been ascertained, and it was known that 

 muscles, nerves and tendons were composed of threads or 

 fibres, that the blood- and lymph-vessels were tubes, that the 

 parts which we call fasciae and aponeuroses were thin 

 membranes, and so on. 



Early in the present century Xavier Bichat, one of the most 

 brilliant men of science during the Napoleonic era in France, 

 published his " Anatomic Generale," in which he formulated 

 important general principles. Every animal is an assemblage of 

 different organs, each of which discharges a function, and acting 

 together, each in its own way, assists in the preservation of 

 the whole. The organs are, as it were, special machines situated 

 NO. 1610, VOL. 62] 



in the general building which constitutes the factory or body of 

 the individual. But, further, each organ or special machine is- 

 itself formed of tissues which possess different properties. Some, 

 as the blood-vessels, nerves, fibrous tissues. &c., are generally 

 distributed throughout the animal body, whilst others, as bones, 

 niuscles, cartilage, &c., are found only in certain defir>ite 

 localities. Whilst Bichat had acquired a definite philosophical 

 conception of the general principles of construction and of the- 

 distribution of the tisjuis, neither he nor his pupil Beclard' 

 was in a position to determine the essential nature of the 

 structural elements. The means and appliances at their dis- 

 posal and at that of other observers in their generation were 

 not sufficiently potent to complete the analysis. 



Attempts were made in the third decennium of this century ta- 

 improve the methods of examining minute objects by the manu- 

 facture of compound lenses, and by doing away with chromatic 

 and spherical aberration, to obtain, in addition to magnification 

 of the object, a relatively large flat field of vision with clearness 

 and sharpness of definition. When in January 1830 Joseph 

 Jackson Lister read to the Royal Society his memoir "Or> 

 some properties in achromatic object-glasses applicable to the 

 improvement of microscopes," he announced the principles on 

 which combinations of lenses could be arranged, which would 

 possess these qualities. By the skill of our opticians, micro- 

 scopes have now for more than half a century been constructed 

 which, in the hands of competent observers, have influenced 

 and extended biological science with results comparable to- 

 those obtained by the astronomer through imfMrovements in the 

 telescope. 



In the study of the minute structure of plants and animals the 

 observer has frequently to deal with tissues and organs, most of 

 which possess such softness and delicacy of substance and outline 

 that, even when tnicroscopes of the best construction aie em- 

 ployed, the determination of the intimate nature of the tissue, 

 and the precise relation which one element of an organ bears to 

 the other constituent elements, is in many instances a matter of 

 difficulty. Hence additional methods have had to be devised' 

 in order to facilitate study and to give precision and accuracy to 

 our observations. It is difficult for one of the younger genera- 

 tion of biologists, with all the appliances of a well-equipped' 

 laboratory at his command, with experienced teachers to direct 

 him in his work, and with excellent text-books, in which the 

 modern methods are described, to realise the conditions under 

 which his predecessors worked half a century ago. Labora- 

 tories for minute biological research had not been constructed, 

 the practical teaching of histology and embryology had not beerv 

 organised, experience in methods of work had not accumulated ;. 

 each man was left to his individual efforts, and had to puzzle 

 his way through the complications of structure to the best of his 

 power. Staining and hardening reagents were unknown. The 

 double-bladed knife invented by Valentin, held in the hand, was 

 the only improvement on the scalpel or razor for cutting thin, 

 niore or less translucent slices suitable for microscopic examina- 

 tion ; mechanical section-cutters and freezing arrangements had' 

 not been devised. The tools at the disposal of the microscopist 

 were little more than knife, forcepvs, scissors, needles, with 

 acetic acid, glycerine and Canada balsam as reagents. But 

 in the employment of the newer methods of research, care has 

 to be taken, more especially when hardening and staining re- 

 agents are used, to discriminate between appearances which are 

 to be interpreted as indicating natural characters, and those 

 which are only artificial productions. 



Notwithstanding the difficulties attendant on the study o. the 

 more delicate tissues, the compound achromatic microscope pro- 

 vided anatomists with an instrument of great penetrative power. 

 Between the years 1830 and 1850 a number of acute observers 

 applied themselves with much energy and enthusiasm to the 

 examination of the minute structure of the tissues and organs ir» 

 plants and animals. 



Cell Theory, 

 It had, indeed, long been recognised that the tissues of 

 plants were to a large extent composed of minute vesicular 

 bodies, technically called cells (Hooke, Malpighi, Grew). In 

 1831 the discoveiy was made by the great botanist, Robert 

 Brown, that in many families of plants a circular spot, which he 

 named areola or nucleus, was present in each cell ; and in 1838 

 M. J. Schleiden published the fact that a similar spot or nucleus 

 was a universal elementary organ in vegetables. Iri the tissues 

 of animals also structures had begun to be recognised compar- 

 able with the cells and nuclei of the vegetable tissues, and in. 



