320 SUMMARY OF CURRENT RESEARCHES RELATING TO 



in order to indicate that tliose particnlar specimens present noteworthy 

 features. 



The method may be elaborated in a variety of ways for the record- 

 ing of nemas, rotifers, protozoa, desmids and a vast array of other 

 microscopic objects. If the charts are of card-system size, say 5 in. by 

 8 in., they lend themselves to all sorts of convenient methods of filing. 

 By using thin paper, carbon copies can be made at the original draft. 



•The charts can he made and used by a grade of assistant that might 

 hardly be entrusted with the use of a recording mechanical stage, and 

 who may lack training in the accurate reading of scales and the record- 

 ing of numbers. Floating of the objects, of course, disarranges them, 

 Newly made slides are sometimes subject to this disadvantage. The 

 difficulty is avoided by keeping the slides always in a horizontal 

 position. 



Objpci Suppoji for a Freezing Microtome. — ^In this freezing microtome 

 attachment, the object is to reduce the metal parts to a minimum and 

 to concentrate the effects of the freezing mixture as much as possible 

 upon the object to be frozen. To this end the object is placed on a 

 thin metal plate, only about one to three thousandths of an inch thick, 

 to which the necessary rigidity is imparted either by soldering it to a 



radiating framework in the form of a flat wheel sawed from somewhat 

 tliicker metal, or, preferably, by giving to the metal the form of a dome. 

 These metal supports are illustrated in fig. 2 and fig. 3, in which they 

 are shown full size. A six-spoked wheel, having a hub-hole one-eighth 

 of an inch across, is sawed from a sheet of German silver about one 

 two-hundredth of an inch thick. The edges of the central aperture 

 are bevelled so that the mixture frozen on it becomes dove-tailed to the 

 plate. In a similar way, the small, washer-shaped piece of German 

 silver fastened to the top of the dome, as shown in fig. 3, r, is also 

 bevelled. 



The German silver wheel is soldered throughout to a round sheet 

 of exceedingly thin brass or German silver. Then into six marginal 

 perforations in the German silver wheel, brass pins are soldered, giving 

 to the whole affair the appearance of a six-legged table. The heads of 

 pins are filed off so as to give clearance for the microtome knife. The 

 pins serve to fasten the plate to a perforated cork, being thrust into the 

 cork as shown in the illustration. The rim of the dome of thin sheet 

 metal is somewhat similarly stiffened Ijy soldering to it a ring of German 

 silver which is perforated and supplied with six brass pins in the 

 manner just described. 



Though the dome form is somewhat more difficult to construct than 



