1888.] MICROSCOPICAL JOURNAL. 201 



with chromic salts an elective differentiation, the medullary sheath being rose- 

 colored, nuclei of nerve and neuroglia cells and the vascular cells being violet. 

 Further, he discovered that the nuclular substance would not stain if the 

 nerve had been diseased, and at a time when no mode of tracing diseased 

 nerves was known. But since his method does not always perfectly distin- 

 guish the medullary sheath, the color diflerence not being well enough dis- 

 played, a modification of his method is proposed which has proved valuable. 

 The hardening of brain or cord having been effected in Midler's fluid, or am- 

 monium bichromate, the reagent is not to be washed out with water. Sections 

 must be transferred at once from alcohol to a concentrated watery saturated 

 solution of safranin, where they are to be overstained (24 hours). From the 

 staining fluid the section must be transferred to alcohol, where they are gently 

 agitated until the grey substance begins to be unlike in color to the white 

 substance, when, with a thick glass rod, the section must be transferred to a 

 weak solution of a metallic salt — gold chloride or platinic chloride (j^jy or 

 TcrVo')' Here the section must remain until the grey substance has assumed a 

 violet tint. If the section remains too long in this solution, the staining will 

 prove a failure. From the gold solution the section is transferred to alcohol, 

 and left there till the grey substance has assumed a rosy-violet color and the 

 white substance forms a distinct red ground. Then the section is mounted in 

 balsam in the usual way, and it will show a far clearer differentiation of its 

 different parts than when stained by the customary safranin method. 



Studies for Beginners. — IV. 



By H. L. OSBORN. 



THE YEAST PLANT — (Conhnucd J/'Of/l />. 86). 



5. An experiment. — To follow the present article and to prove by obser- 

 vation the facts which will be stated, the student should procure some fresh 

 yeast, and for 48 hours allow some to stand in a thin solution of sugar and 

 water; also, some in rain-water. The yeast in both cases will be noticeable 

 as a white sediment upon the bottom of the cup or tumbler. For microscopic 

 examination, a drop of this sediment may be taken up with a dropping-tube 

 and be deposited upon a slide. Cover it with a glass circle and examine with 

 a power of 350 diameters. But, before this microscopic examination is made, 

 first notice some of the facts which can be learned with the naked eye. After 

 48 hours, particularly if they have been kept mildly warm (70° to 80° F.), 

 the contents of the cups show a marked difference. One is turbid and bub- 

 bles arise to the surface ; it is no longer sweet, but is becoming sour, and will 

 become quite so. If means of testing were at hand considerable alcohol 

 would be found to have in some way gotten into the water. In the other 

 cup nothing of this sort is to be found. The water remains clear, does not 

 become sour, and does not contain alcohol. Obviously something has taken 

 place in the sugar solution due to the presence of the sugar, for both prepara- 

 tions are by design alike, except as regards the sugar. In the laboratory at 

 Hamline University last spring, while some students were at work upon yeast, 

 they kept their solutions in corked vials. Invariably, after a time, the corks 

 were blown out of certain vials with loud explosive reports. This never 

 happened with those containing pure rain-water and yeast. The two may 

 now be compared microscopically. 



6. Yeast from the sugar solution. — In making the mount for examina- 

 tion caution must be taken not to have the yeast too thick. Put on a drop of 

 water with the yeast, and add another drop of clear water if the yeast looks 

 very thick. Examination will now reveal a very different looking yeast plant 



