ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 671 



free end of the paper strip, wliich is well saturated with bergamot oil, is 

 allowed to dip into a capsule of this oil. The surface of the celloidin 

 block is then brushed over with absolute alcohol, the section made and 

 transferred to the oil, from which it is picked up by the needle and 

 arranged on the paper strip. When the required number of sections 

 have been duly placed in position on the strip of paper, the latter is 

 drained. The paper is then laid, the section side downwards, on a 

 carefully dried slide, and then dried with blotting-paper. The paper 

 strip is then carefully removed by rolling it off from one end or corner. 

 If a section should stick to the paper the surface may be moistened with 

 the oil again, and the strip pressed down again, and if this fail it must 

 be taken with a brush and placed in its proper position. When all the 

 sections are properly arranged, the surface is smoothed down and all 

 the oil removed with smooth blotting-paper. The balsam is then 

 applied, and the cover-glass imposed. 



The sections, in order to prevent decoloration, should not be allowed 

 to get too near the edge of the cover-glass. In imbedding long objects 

 as certain worms, the process may be hastened by imbedding tirst the 

 whole object and then cutting it into pieces and arranging these in their 

 proper order in a second imbedding, so that one action of the knife 

 produces ten to twenty sections serially arranged. 



Proper Thickness of Microscopical Sections.* — Nowadays, says the 

 Editor of the ' Microscope,' it seems to be the aim of many possessors 

 of good microtomes to cut their sections as thin as possible, e. g. from 

 1/2000 to 1/4000 of an inch in thickness. The origin of this fashion of 

 cutting over-thin sections is difficult to determine, for such sections are, 

 in the majority of cases, quite useless for any purpose of study, and the 

 time involved in their preparation is as good as wasted. It is probably 

 due to a desire to exhibit one's skill without regard for utility — something 

 like that which induces one to write 10,000 words on a post-card, simply 

 because some one else has succeeded in writing 9000. 



Friedlander in his excellent little ' Manual of Microscopical Tech- 

 nology,' raises the following objections to sections of extreme thinness : — 

 " (1) They are manipulated with difficulty and considerable time is often 

 lost in spreading them on the slide. (2) The various elements contained 

 in the meshes of these sections are very apt to fall out, and as these are 

 generally of extreme importance, the object of the examination may be 

 defeated. (3) Structures which are sparingly distributed throughout an 

 organ, as, for example, animal and vegetable parasites, are naturally more 

 apt to be discovered in thick sections. (4) In thick sections definite 

 stereometric conceptions of the structure of an object are frequently 

 obtained, inasmuch as several superimposed strata are scanned directly, 

 in situ et in continuo, while with extremely thin sections plane images 

 alone appear." For sections of fresh organs he recommends a thickness 

 of from 1/500-1/250 in. ; for hardened preparations from 1/2500 to 

 about 1/850 in. The rule should be, then, not to make sections as 

 thin as possible, but rather to have them of a thickness that will include 

 as many layers as can be clearly studied. 



Preparing Sections from Test-tube Cultivations.f — Prof. A. Neisser 

 first warms the test-tube containing the cultivation, so that the gelatin 



* The Microscope, viii. (1888) pp. 147-8. 



t Centraibl, f. Bacterid, u. Parasitenk., iii. (1888) pp. 506-10. 



