322 SUMMARY OF CURRENT RESEARCHES RELATING TO 



mount ou the stage of a microscope, bring the object into focus, and 

 with a dissecting needle gently shove the cover-glass slightly back and 

 forth until the object is seen to be on end. Allow to remain on the 

 stage of the microscope until the jelly sets, watching from time to tiuie 

 to see that the object maintains the desired position. 



According to my experience, this is a better method of obtaining 

 end-on and sectional views of the heads of free-living nemas and other 

 similar small organisms than that of sectioning and embedding. The 

 trouble with the method of sections is that the microtome knife very 

 seldom cuts the object to advantage. It is quite likely to cut in the 

 wrong place. If the ends of the setse or the surfaces of the lips are 

 removed in the first cut, it is a very troublesome matter to oljtain a 

 good view or good sketch of the structures. Even if some of the parts 

 should not be lost or offer difficulty in mounting, there are so many 

 chances that the microtome blade will cut through at a disadvantageous 

 place that, as a rule, a very considerable number of nemas will have to 

 be sectioned before a good preparation is secured. 



The method of sections has the further disadvantage that the 

 following of such small objects through the various dehydrating and 

 staining fluids, and the final orientation of them, is a tedious and diffi- 

 cult matter. Moreover in the case of nemas, there is considerable 

 difficulty in properly embedding the object. The cuticle of nemas is so 

 impenetrable that unless special precautions are taken, the paraffin will 

 not thoroughly penetrate the tissues, and the results will be unsatis- 

 factory. 



End views may be obtained by mounting the nemas in a microscopic 

 well made from a thin section of thermometer tubing. The tubing 

 should be like that used in the most delicate medical thermometers, 

 that is to say, with the smallest aperture procurable. This tubing may 

 be bouo'ht under the name thermometer, or barometer tubino-. It is 

 well to have on hand ground sections of varying thickness, from one- 

 quarter of a millimeter thick to one millimeter or more. The discs 

 are cemented to a glass microscope slide at the time of using by means 

 of smoking hot was or other suitable cement. Before cementing the 

 disc to the slide, fill the capillary aperture in the disc with mounting 

 fluid. This may he easily done by placing on the slide a very tiny 

 drop of the mounting fluid, and laying the disc on to the small drop. 

 The mounting fluid will enter the aperture by capillarity. If it be 

 desired to look at the head end of a nema, it is placed in the microscopic 

 well, tail down. If the nema is too long for the well, it may be cut 

 to fit it. The point is, to see tliat the object has about the same length 

 as the depth of the well, so that the end portion of the object it is 

 desired to view will come close to the under side of the cover-glass 

 when this latter is placed on the top of the well, or rather on the disc 

 of the glass containing the well. In. placing the nema in the well, a 

 suitable tool is a small, curved hair cemented to the end of a dissecting 

 needle. Human eye-ljrow hairs are suitable for this purpose. Using 

 this method, the specimen can be examined in clove oil, cedar oil, or 

 any mixture of these or any other similar thin mounting fluid. Oedar 

 oil, having the same refractive index as the glass composing the well. 



