54 PRACTICAL HISTOLOGY. 



teristic of these fibres. The fibres consist of cellulose. 

 Unlike starch, it is not rendered blue by iodine, but acquires 

 a brownish - yellow tinge like that of the iodine solution 

 itself. 



b. Allow a drop of dilute sulphuric acid (acid and 

 water equal parts) to flow under the cover-glass. The fibres 

 soon become swollen, and acquire a blue colour. If the 

 blue colour be slow in appearing, add a small drop of strong 

 sulphuric acid to that already on the slide. The reaction 

 takes place equally well if the acid be added before the 

 iodine. 



68. Linen Fibres. (H.) Examine in water. Unlike 

 cotton fibres, they have no twist. They are for the most 

 part solid, with here and there a crevice running along their 

 interior. 



69. Disc-bearing Tissue. (H.) Make, with the aid 

 of a scalpel, an excessively thin vertical section of an ordi- 

 nary cedar pencil, or of a piece of common fir. Examine 

 in water, and observe the disc-like depressions on the fibres. 



70. Bacteria. (H.) These maybe readily developed 

 in an infusion of some albuminoid matter e.g., muscle. 



a. Mince some lean meat, and allow it to soak in cold 

 water for an hour ; squeeze it in the water with the hand ; 

 filter through calico, and then through paper. Place the 

 filtrate in a hot chamber, or near the fire, to keep it at 

 summer heat, for thirty-six hours or so. A pellicle forms 

 on the fluid. 



b. Place a particle of the pellicle with a small drop of 

 the surrounding fluid on a slide ; cover, and examine. 



The pellicle consists of very minute, clear, motionless 

 granules. These are young bacteria. They are imbedded 

 in a clear jelly-like matter, that is, however, difficult to 

 see unless a dye be used. In the fluid around the pellicle, 

 the bacteria are in active motion. The minute granular 

 bacteria dance about in directions that are indefinite, like 

 the granules of gamboge already examined. The elongated 

 bacteria exhibit, as long as they are alive, movements in a 

 definite direction. They shoot across the field with great 

 rapidity. 



