ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 339 



MICEOSCOPY. 



A. Instruments, Accessories, etc.* 

 C3) Illuminating: and other Apparatus. 



Sedgwick-Rafter Ocular Micrometer. f — C. E. Turner, who describee 

 this micrometer, states that it is sub-divided, and when used with an 

 ocular of the No. 4x Spencer type (2-inch) and a 16-mm. objective can 

 be so standardized by the aid of a stage micrometer that the large 

 square will outline a square millimetre surface. The smallest square 

 will then be 20 micra on a side, and the micrometer will form a con- 

 venient measure for larger microscopic objects. By only a slight change 

 in the tube length a standardization with the 4-mm. objective can be 

 made, which will increase the magnification five-fold, thereby reducing 

 the side of the large square to 200 micra, and that of the smallest square to 

 four, so that with the high power the dimensions of all but the very 

 smallest microscopical organisms can be readily obtained. There is also a 

 marked advantage in the way it is ruled into squares of various sizes. 

 It enables one to measure the length and the breadth of an object at 

 the same time, and yet leaves the greater part of the field of vision 

 relatively free from lines interfering with clear definition of objects. 

 Ocular micrometers may be made by engraving or photography. In 

 either case the actual size of the large square ruled on the glass should 

 be 7 mm. on a side. The advantages of this type of micrometer are its 

 ready adaptability to general use with high or low powers of the 

 microscope ; the definition of measured squares or unit surfaces which 

 are easier to use and to fix in mind than are linear units ; a comparatively 

 unobstructed field, and in the photographic product, low cost. 



Polarized Light for Detecting Foreign Bodies in Wounds.:}: — A. 

 Policard and B. Desplas, who had not(;d the great frequency of 

 microscopic foreign bodies (fragments of clothes, particles of wood, &c.} 

 in healthy wounds, particles invisible to the naked eye and very difficult 

 to make out in sections when placed under the microscope, find that 

 these foreign bodies are easily located under polarized light. All such 

 foreign bodies are birefringent. When the Nicols are crossed they 



* This subdivision contains (1) Stands ; (2) Eye-pieces and Objectives ; (3) 

 niuDfiinating and other Apparatus ; (4) Photomicrography ; (5) Microscopical 

 Optics and Manipulation ; (6) Miscellaneous. 



t Trans. Amer. Micr. Soc, xxxv. (1916) pp. 186-8 (1 fig.). 



J C.R. Soc. Biol. Paris, Ixxx. (1917) pp. 248-9. 



