110 ATLAS OF BIOLOGY. 



Transfer the sections as cut, together with the imbedding material in which they lie, to a slide, the 

 surface of which has been previously painted over with a heated solution of white shellac in kreasote. 

 Submit the whole to the temperature of the melting-point of the paraffin, until the kreasote is evaporated, 

 when the sections will become firmly adherent to the shellac. The slide must next be immersed in turpentine, 

 which will dissolve up the remaining imbedding material, thus leaving the sections fixed in place and ready 

 to be covered with Canada balsam. 



For final mounting well-powdered Canada balsam, first thoroughly dried, must be dissolved in benzole or 

 chloroform, to the consistency of glycerine. A drop of the balsam thus prepared should be deposited upon the 

 slide by means of a glass rod, and allowed to diffuse itself among the sections ; the cover-slip should then be 

 let down gently and obliquely upon the objects, its under surface first having been smeared with Canada 

 balsam. 



Under the above method of preparation the sections may be cut with a dry razor, but where, as in the 

 case of vegetable stems, etc., they are to be taken from material which has not been submitted to any such 

 treatment, both razor and preparation must be kept moistened during the process with the fluid in which the 

 preparation has been preserved. 



Fresh preparations of animal tissues, when not frozen, must always be examined in serum or normal salt 

 solution. For the examination of fresh vegetable tissues, water will suffice. 



The microscope used in making the drawings for this volume was one by Zeiss of Jena, and in the 

 formulae given in the text (example D. 2) the letter refers to the eye-piece, and the numeral to the objective 

 employed. 



In no case should a high-power eye-piece be resorted to unless absolutely indispensable, as the sharpness 

 of definition obtained by low ones, such as Zeiss 2 or 3, is highly desirable. 



A micrometer of some kind is indispensable to the student of histology, and the purpose to be aimed at 

 in its use, is that of a knowledge of the size of the objects under examination, rather than that of merely 

 ascertaining the magnifying power of the microscope. Most satisfactory results are to be obtained by using 

 an eye-piece micrometer ruled in squares, and by drawing both these and the object to the proportions 

 observed. Having thus a record of objects, drawn in proportion relative to squares of unknown value, it 

 remains but to ascertain the dimensions of these. This is best done by using, in conjunction with the 

 eye-piece micrometer mentioned above, a stage micrometer, ruled to known intervals, whereupon there will be 

 superposed lines of known and unknown value. The actual value of the squares of the eye-piece micrometer 

 may now be once for all calculated, and a record kept of the same for each lens combination. 



H. Preparations of shells and similar hard parts are best made as follows : 



A small piece of the structure to be prepared should be first isolated, and then cemented with Canada 

 balsam to a piece of plate glass. When quite set it can be ground down on a rough surface to the required 

 thinness, and finally dislodged for mounting, by submerging the whole in benzole. It may then be put up in 

 Canada balsam in the usual manner. 



I. For object-glass culture it is best to use either a small cell of the ordinary type, or a slide which is 

 excavated. Filling this with the nutritive fluid water for protococcus, Pasteur's fluid for the moulds, sugar- 

 solution for the pollen-grain, etc. next introduce the organisms upon which observation is to be made, and 

 place a cover-slip over the whole, the edges of which should be oiled to check evaporation. If the observation 

 be a prolonged one, it is well to place the nutritive medium in communication with a reserve of the same 

 fluid, by means of a cotton thread. 



