The President's Address. By Prof. P. Martin Duncan. 183 



want of scientific care are the temptations to and the causes of this 

 very frequent source of error, which is intensified by the common 

 fault of want of perfect flatness of the plane surface of the stand. 



The beautiful adaptation of a sliding glass restricted by a point, 

 whilst it reheves the microscopist from the expenditure involved by 

 a complicated brass movement, is so easily fitted that there is no 

 excuse for employing the fingers alone. 



Some very remarkable communications have been made to the 

 Society during the past twelve months, and one in particular marks 

 an epoch in the science of microscopy. Whoever would have 

 thought a few years ago of mounting objects in such media as 

 bisulphide of carbon and phosphorus, and a solution of biniodide 

 of mercury and iodide of potassium ? Mr. Stephenson's paper 

 places the results of these solutions before the world, and his intro- 

 duction is explanatory of the philosophy of the relation of the 

 refractive media in which the object is mounted, to the numerical 

 aperture of the objective. 



Almost as important as these new media, are the instruments 

 which have been described in our Journal for slicing preparations. 

 Some of these are marvels of ingenuity, and especially that one 

 which employs the freezing apparatus as an adjunct. 



Mr. Michael has continued his remarkable studies of the British 

 Oribatidae, and it is difficult to know which to admire most, the 

 beautiful construction of the objects or the extreme care and 

 ingenuity displayed in dissecting and mounting them. 



The direction of microscopic research, however, has not been so 

 much amongst the higher invertebrata, although great work has 

 been done in them, as in relation to those legions of microscopic 

 beings which are now shown to be a fertile source of misery to the 

 human race. The most careful researches of old and the former 

 study of the pathology of many fatal, so-called constitutional, diseases 

 failed to bring their cause before the practitioner. Yet common 

 sense and great experience had indicated to Holland, in the early 

 part of this century, that germs or living entities were a vera causa. 

 It required the present perfection of the Microscope and the 

 development of the method of preparation and colouring to demon- 

 strate bacteria in the tissues, to identify the bacteria of special 

 diseases, and last, not least, to exhibit plainly and definitely the 

 bacteria of phthisis pulmonalis. 



Eesearches on the bacteria of septicaemia by Mr. Dowdeswell, 

 on organisms in the excreta of animals and birds, and in ice, by 

 Dr. Maddox, have appeared in the pages of the Journal, and they 

 form but a small fraction of the immense literature of these lowly 

 organized things. Certainly the Microscope has not done all in 

 these investigations, for an elaborate chemistry has enabled skilled 

 workers to stain and decolour, the bacteria remaining tinted. 



