8 REPORT— 1900. 



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, more or less translucent slices suitable for microscopic 

 examination ; mechanical section-cutters and freezing arrangements had 

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

 little more than knife, forceps, scissors, needles ; with acetic acid, glyce- 

 rine, 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 reagents are used, to discriminate between 

 appearances which are to be intei'preted as indicating natural characters, 

 and those which are only artificial productions. 



Notwithstanding the difficulties attendant on the study of the more 

 delicate tissues, tlie compound achromatic microscope provided anatomists 

 with an instrument of great penetrative power. Between the yeai'S 1830 

 and 1850 a number of acute observei's applied themselves with much energy 

 and enthusiasm to the examination of the minute structure of the tissues 

 and organs in 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 discovery was made by the 

 great botanist, Robert Brown, that in many families of plants a circular 

 spot, whicli 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. In the tissues of animals also 

 structures had begun to be recognised comparable with the cells and nuclei 

 of the vegetable tissues, and in 1839 Theodore Schwann announced the 

 important generalisation that there is one universal principle of develop- 

 ment for the elementary part of organisms, however difierent they may be in 

 appearance, and that this principle is the formation of cells. The enun- 

 ciation of the fundamental principle that the elementary tissues consisted 

 of cells constituted a step in the progress of biological science, which 

 will for ever stamp the century now drawing to a close with a character 

 and renown equalling those which it has derived from the most brilliant 

 discoveries in the physical sciences. It pro\ided biologists with the 

 visible anatomical units through which the external forces operating on, 

 and the energy generated in, living matter come into play. It dispelled 

 for ever the old mystical idea of the influence exercised by vapours or 

 spirits in living organisms. It supplied the physiologist and pathologist 

 with the specific structures through the agency of which the functions of 

 organisms are discharged in health and disease. It exerted an enormous 

 influence on the progress of practical medicine. A review of the progress 

 of knowledge of the cell may appropriately enter into an address on this 

 occasion. 



