1888.] • MICROSCOPICAL JOURNAL. 85 



Studies for beginners. — II. 



By H. L. OSBORN. 



THE YEAST PLANT — ( Continued fvom f. 42 J 



1. Protoplasm — This, as you look at it through the microscope, seems 

 like a very fine-grained substance pervading the entire yeast. It is so nearly 

 transparent that you may at first think that there is nothing there, but this 

 delusion you may correct by searching until you find a dead yeast cell, from 

 which the protoplasm has dissolved. You can also demonstrate the presence 

 of the protoplasm by ' staining ' with iodine. Iti staining, you may easily 

 make the mistake of not allovs^ing the fluid time enough to operate. This will 

 depend on the strength of your solution, and may be a quarter of an hour or 

 more. The protoplasm is the living substance of the yeast cell, and, after the 

 parts of the cell have been demonstrated, I shall return to it for further re- 

 mark. In working out all these points, remember that you are dealing with 

 very small bodies and must use high powers and great patience. 



2. The cell-wall. — This can be demonstrated best on dead cells or by 

 crushing living, ones. To do the latter thin the yeast so that you have only 

 a very few cells under the cover-glass. Then cut a bit of. blotting-paper the 

 shape of the cover and lay it 011 the cover, then press on the blotter with your 

 finger. You will, perhaps, succeed in pressing upon the yeast cells, which 

 are spherical, hard enough to burst the wall and liberate the contents. You 

 can now mount your slide on the stage of the microscope and search for one 

 of the yeast cells. The search had better be conducted with the low power, and 

 when a cell is found it should be left in the centre of the field while the high 

 power is adjusted. Examination of the crushed yeast cell will show the 

 wrinkled cell-wall and, very likely, some of the protoplasm spread about the 

 break, and the empty yeast cell. In living yeast the cell-wall appears as a 

 narrow band with two lines defining it outside the protoplasm. 



3. The vacuole. — This is a round spot, of greater or less size, inside the 

 protoplasm. It looks like an empty space surrounded by the protoplasm. In 

 size it varies from a quarter of the diameter of the yeast cell to a half, or even 

 more. There may be one, two. or even three vacuoles in one yeast cell. If 

 so, they are all spherical and surrounded by the protoplasm. That the vacu- 

 oles are surrounded by the protoplasm is shown by the fact that you can see 

 the protoplasm all around them, and then by focusing up above them or 

 down through them you can see the protoplasm over and under them. The 

 vacuoles are not really empty spaces, but are bubbles of water in the proto- 

 plasm — water which contains some soluble matters and is really sap. It is 

 probable that the size of the vacuole increases with the age of the cell, and it 

 is a fact that some cells can be found in which the vacuole extends almost to 

 the cell-wall, leaving but little protoplasm inside the wall. 



4. The fat droplets. — In addition to numerous very minute specks in the 

 protoplasm, you can usually find in the yeast cells a few somewhat larger, 

 but very small, very bright or (according to focus) very black spots. These 

 are little droplets of fat. Their presence in large amount would argue ill- 

 health of the cell or fatty degeneration, but a small quantity is naturally pres- 

 ent on all occasions. 



It may seem incredible to one unused to studying minute organisms to hear 

 that ' those specks' show so much, but they positively reveal to any student, 

 who approaches them aright, everything described and very much more be- 

 sides. Any one, then, of our yeast cells, from the immense number in a cake 

 of ' compressed yeast,' is a little oval body with a protoplasmic substance, an 

 outside coat or jacket, a cavity of sap, and some drops of fat. Take a few 



