82 BIOLOGY 



and those of animals. These are pathogenic bacteria or disease 

 germs. They cause many of our most serious contagious 

 diseases like typhoid fever, tuberculosis, diphtheria, blood poison- 

 ing, etc. Thus, although they are extremely minute, bacteria 

 are agents of great importance in the world. It is hardly 

 possible to imagine anything more simple in structure, but 

 at the same time of greater importance, than bacteria. 



LABORATORY WORK 



The best method of obtaining material for laboratory work is to place 

 in a number of glass jars or shallow dishes pond-lily leaves, leaves of other 

 plants, algae of various kinds, or any other decaying organic material 

 from ponds and ditches. Fill the dishes with water and allow them to stand 

 undisturbed from one to several weeks. Various kinds of microscopic 

 organisms will appear in the different dishes, from which the desired organ- 

 ism can be chosen. 



Amoeba. A brown scum will usually appear in a few days on the surface 

 of the water covering the decaying organic material which is likely to contain 

 Amcebce. When this scum is scraped from the leaves and studied under a 

 1/6 inch objective it will usually disclose small specimens of Amoeba. The 

 animals should be studied alive and without any special treatment, since 

 they are sufficiently transparent, and slow enough in their movements to 

 show all the points in their anatomy, and nearly all the features mentioned 

 in the text may be seen without difficulty. 



Paramedum. These may be found in abundance in the scum from the 

 decaying pond weeds after they have been left for a week or more. Many 

 white, moving bodies, just visible to the naked eye, will be found in a drop 

 of this scum, which should be studied with a 1/6 inch objective. The chief 

 difficulty in studying them is due to their constant motion; various methods 

 of holding them quiet may be used. A bit of filter paper under the cover 

 glass will sometimes hold the individuals quiet in its meshes, or they may be 

 held quiet under a cover glass by supporting it on a small bit of paper, just 

 thick enough to hold them without crushing them. The animals are 

 to be studied alive, and a little patient examination of several specimens 

 will usually show most of the points of structure mentioned in the text. 

 To bring out the nucleus, a very weak aqueous solution of methyl green 

 should be run under the cover glass. If the solution is not too strong it will 

 stain the nucleii green, before affecting the rest of the organism. Animals 



