DETECTION OF ADULTEKATION. 27 



lamp, is required. In addition to the above, a pair of teasing-needles, 

 a pair of small forceps, and a scalpel should be secured. 



As a clearing agent a chloral hydrate solution made up as follows 

 was almost exclusively used: Chloral hydrate, 150 grams; water, 

 100 cc. 



Among other reagents of occasional value the following should be 

 noted: Alcohol of two strengths, 70 per cent and 95 per cent; two 

 grades of glycerin, 100 per cent and 50 per cent (glycerin and water 

 1:1 by volume), and glycerin jelly are needed if permanent speci- 

 mens are to be made, and this will almost always be done by careful 

 workers. 



The glycerin jelly is made up as follows: Best gelatin, 1.5 parts; 

 water, 3 parts, and glycerin, 4 parts. Some persons a prefer to use 

 only 1 part of gelatin, since it gives a jelly more easily worked than 

 the amount mentioned. Soak the gelatin in the water until it is 

 soft, add the glycerin, and heat over a water bath, finally adding two 

 or three drops of carbolic acid as a preservative. 



TECHNIQUE. 



The difficulty encountered on examining specimens mounted in 

 water or glycerin direct is due to the fact that they are too opaque 

 and contain considerable air. Some means of clearing the frag- 

 ments are necessary. Priestman 6 treated the sample with nitric 

 acid, which attacked the more delicate tissues of the leaf first, and 

 if the action was stopped at the right time, the leaf epidermis could 

 be mounted as nearly clean tissues. This method is laborious if a 

 large number of samples is to be tested, and seems to require con- 

 siderable judgment as to just the stage at which the action is to be 

 stopped, and hence is not desirable unless one is very familiar with 

 microscopical technique. 



In this work the chloral hydrate solution before mentioned was 

 used. A small amount of the specimen is placed upon a slide with 

 two or three drops of the solution and gently heated to boiling over 

 the micro-bunsen burner or alcohol flame and kept gently boiling 

 for about one minute. If the chloral hydrate solution boils away 

 before the heating is finished, a few drops more are added, for if the 

 specimens become dry the object of the treatment is defeated. After 

 the boiling is completed the specimen is allowed to cool down some- 

 what, a cover-glass is placed over it and the specimen is ready for 

 examination. If too much of the original specimen has been used, 

 the mass will be too dense to give satisfactory results. A few tests, 

 however, will demonstrate to the worker the most satisfactory amount 



Clark's Practical Methods in Microscopy, 2d edition, 1896, p. 243. 

 6 Loc. cit. 

 117 



