Microorganisms in Relation to Man 



563 



tacked. Possibly the solutions in the test tubes may help in 

 solving the problem. 



Exercise. Examine the test tubes, tasting and smelling the con- 

 tents of each and recording the results. Is the preparation which was 

 not heated, sour or acid ? Let it remain after testing, as directed, to 

 see whether or not it will eventually become vinegar. When bubbles 

 are rising freely, take a few drops with a medicine dropper from near 

 the bottom of the tube, and put them on a glass slide for examination 

 with the microscope. Examine them carefully, record, and make 

 sketches of what you observe. 



281. The yeast plant. Examine in the same way a few 

 drops taken from the yeast mixture and compare the two. 



FIG. 168. Yeast Cell. A, a typical yeast cell with nucleus and several 

 vacuoles which are filled with cell sap. B and C, stages in the process of bud- 

 ding, the nucleus dividing in the formation of the new cell. D, a bud still 

 attached to parent plant, producing a new bud. E and F, formation of spores, 

 the nucleus divided into four, each new nucleus acquiring a cell wall and becom- 

 ing a spore, the parent cell wall serving as a sac. G, a spore developing into a 

 yeast cell which buds and forms a colony. 



What do the results indicate as to the changes which are taking 

 place in each? Do you think the same process is occurring in 

 both? If the microscope is high power enough, it will make 

 clearly visible the minute bodies which produce the changes in 

 the liquids and the yeast mixture. The small bodies which 

 the microscope reveals are egg-shaped or oval, almost trans- 

 parent, and they may be separate or joined in chains or tree- 

 like forms. They may be like the forms shown in Fig. 168. 



