ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 503 



rotation point are brought still closer. The rotary gear consists of a 

 winch-wheel whose axle passes through the base of the bent arm, and 

 by means of two obliquely toothed wheels imparts its motion to the 

 disk. As the winch is turned disk and object rotate with uniform 

 velocity and always in the same direction. The mutual adjustment of 

 knife and object depends upon the drop-movement of the knife, but it 

 is automatic, being an effect of the gear motion transmitted by a micro- 

 meter spindle. This spindle is coupled with another axle, which 

 carries at its upper end a saw-toothed wheel, rotatory by means of a 

 connector. This connector is drawn forward at each rotation of the 

 main disk by means of an eccentric disk fastened near the lower end of 

 the connector in order to slide back afterwards. The number of teeth 

 set in action in the wheel, the consequent drop of the knife and the re- 

 sulting section -thickness are governed by a scale, every division of which 

 corresponds to a thickness of 1T y'oo mm - It ' s possible to cut sections 

 whose thickness may be any integral number of mikrons between 1 fj. 

 and 20 //.. 



(4! Staining 1 and Injecting. 



Differential Staining of Fats.* — E. T. Bell employs a modification 

 of Dietrich's and Ciaccio's stains for demonstration of fat in tissue 

 sections. The technique enables him to distinguish fat droplets 

 consisting mainly of triolein from those droplets that principally contain 

 lipoids. The former appear in annular shape, the latter are quite solid. 

 In the former case the central portion of the droplet is not chromated, 

 and therefore dissolves out in the xylol used in embedding. The 

 technique employed is as follows : — Fix tissue in 10 p.c. aqueous potas- 

 sium bichromate 100 c.cm., glacial acetic acid 5 c.cm. ; wash, dehydrate 

 and embed in paraffin, cut in sections and fasten to the slide with 

 albumin. ' Remove paraffin with xylol and xylol with absolute alcohol 

 and transfer to freshly prepared saturated solution of Sudan III in 

 80 p.c. alcohol for 10 minutes. Rinse off excess of stain with 50 p.c. 

 alcohol and transfer immediately to water to stop action of the alcohol. 

 Counterstain with Delafield's hematoxylin and wash in water, differen- 

 tiate with acid alcohol, wash and mount in glycerin-gum arabic. 



New Hematoxylin Solution. t — A. von Szuts recommends the 

 following modification of Mallory's phosphomolybdate or phosphc- 

 arsenate stain, which latter, although giving very beautiful results, 

 especially in the investigations of nervous tissues, has the disadvantage 

 of being somewhat expensive. The composition of the new solution is 

 as follows: — 1 p.c. watery hematoxylin solution 100 c.cm., 10 p.c. 

 ammonium molybdate solution 25 c.cm. For fixation of sections of the 

 central nervous system of Vertebrates formol-alcohol or formalin is 

 suggested. After staining for one or two minutes, wash with distilled 

 water and blue in strongly alkaline tap water for about five minutes. A 

 metachromatic effect is produced by variation in the time of blueing of 



* Joum. Path, and Bact., xix. (1914) pp. 105-13 (1 pi.). 

 t Zeitschr. wiss. Mikrosk.. xxxi. (1914) pp. 17-18.^ 



