1892.] MICROSCOPICAL JOURNAL. 141 



An Interesting Study of Living Micro-Organisnis. 



By HENEAGE GIBBES, M. D. 



A very instructive investigation into the life-history of some of 

 the micro-organisms may be made at this time of year with little 

 trouble. Obtain a lump of frog spawn, about the size of the fist, 

 from any of the stagnant pools where these animal live and place 

 it in a glass jar containing about eight or ten gallons of river water. 

 A glass jar suitable for the purpose can be arranged by taking a 

 large bell glass or shade having a knob at the top, such as are used 

 to cover plants, and getting a round piece of wood turned with a 

 hollow in the centre to receive the knob of the glass jar. It can 

 then be inverted in the piece of wood, and, when filled with water, 

 will be perfectlv stead V. The glass of which these bell shades 

 are made is quite thick and well able to stand the pressure of the 

 water. There are other forms of glass jars that will do equally 

 well, but the above is the most inexpensive. Fill the jar nearly 

 full of water and place the frog spawn in it. If it is living it will 

 float level with the surface of the water. The jar should be placed 

 where it can receive full light all day, but not direct rays from the 

 sun. After a few days the small black specks in the eggs will be 

 noticed to be changing their shape and becoming elongated, and 

 this will go on until a number have left the spawn and have at- 

 tached themselves to the sides of the glass as small tadpoles. This 

 will go on until all the eggs that are fertile have given forth tad- 

 poles and hundreds of the little animals are seen sticking to the 

 sides of the glass. For the success of the experiment it is neces- 

 sary that the spawn and water should be placed in a clean jar and 

 not in one where water has been standing for some time and a 

 growth of algae has begun on the sides of the jar. Before all the 

 tadpoles are hatched out, if they are in large numbers, the oxygen 

 in the water will have become exhausted, and if no water plants 

 have been placed in the jar they will all die. This is die result that 

 is wanted, and therefore no plants must be placed in the water. 

 On carefully examining the water from day to day it will be no- 

 ticed that when a large number of tadpoles are clinging to the 

 sides of the jar, although all are not hatched out, a faint milky 

 tinge will be seen in the water ; this rapidly increases ; at the 

 same time the frog spawn falls to the bottom of the vessel and all 

 the tadpoles die. 



Now take a small drop of the water and examine it under the 

 microscope. It will be found to be teeming with countless num- 

 bers of a large spirillum. These resemble two spirals of a cork- 

 screw and are all in rapid motion, going round and round as they 

 move across the field of the microscope. A few other forms will 

 be found, such as infusoria, but the spirilla outnumber them by 

 thousands to one. In some cases a smaller and more slender form 



