52 PRACTICAL HISTOLOGY. 



serve its movements : in the threads, it streams in some 

 towards, in others from, the nucleus. The whole mass of 

 the protoplasm, clear substance as well as granules, moves. 



b. Apply heat with the aid of a warm stage. The 

 simple tin-plate described, 259, Fig. 47, will answer the 

 present purpose. A gentle elevation of the temperature 

 hastens the protoplasmic movement, probably by accelerat- 

 ing chemical changes on which the movement in some way 

 or other most likely depends. If the temperature be raised 

 too high, however, the movement entirely ceases, owing to 

 death of the protoplasm. 



64. Germinating Yeast.* (H.) a. Examine torulae 

 of various sizes. The vacuole seen amidst the protoplasm 

 in the larger torulae must not be mistaken for a nucleus. 



b. Place a drop of magenta solution at the margin of 

 the cover-glass. It stains the buds most rapidly. The 

 protoplasm in many of the torulae becomes stained, while 

 the envelope through which the staining agent must neces- 

 sarily pass to reach the protoplast remains comparatively 

 colourless. A nucleus may be seen in some. The nucleus 

 is generally the part of the cell which is most deeply stained 

 by such agents as carmine, logwood, and magenta. Some 

 torulae never become stained. These are probably the 

 oldest ones. Observe that the envelope is not equally 

 thick in all the torulae. In the youngest (smallest) bud no 

 envelope can be seen. This arises either from the absence 

 or from the excessive tenuity of the envelope. As the bud 

 increases in size, the envelope becomes evident, and grows 

 thicker with advancing age. The envelope is apparently 



* If beer yeast ( Torula cerevisia] cannot be obtained, procure Ger- 

 man yeast, and sow it in sugar and water, or in the following modifica- 

 tion of Pasteur's fluid : 



Magnesium sulphate o - 2 gramme. 



Calcium phosphate 0*2 ,, 



Potassium ,, 0*2 ,, 



Ammonium tartrate 10 ,, 



Cane sugar . 130 ,, 



Water . . SooCC. 



Keep the yeasty fluid gently warmed near the fire, or in a hot 

 chamber for a few hours. 



