554 POWDERED DRUGS 



has been cleaned and sterilized as above directed. By this process the decoction 

 which has adhered to the needle is drawn out in the form of a narrow streak, and 

 if several spores of mucor are present, they will be separated from each other. A 

 single spore may be located with a medium power of the compound microscope, 

 and all other spores present in the streak may be wiped off with a cloth which has 

 been sterilized by heat. Then a drop of the decoction of sterilized horse-dung 

 should be added to the small amount containing the spore on the slide. The slide 

 should be placed in a moist chamber where the spore will soon give rise to a my- 

 celium visible to the naked eye, and from the mycelium numerous sporangia will 

 be produced after a time. The slide may be taken from the moist chamber from 

 time to time and the stages in the development of the fungus examined, but as 

 much care as possible should be taken to prevent the contamination of the culture. 



Knop's nutrient solution, which is particularly good for the culture of algae, 

 consists of 4 parts of calcium nitrate, i part of magnesium sulphate, i part of 

 potassium nitrate, I part of potassium phosphate. These should be dissolved in 

 sufficient water to make a 0.2 per cent, or 5 per cent, solution of the combined salts. 

 The potassium salts should first be dissolved, then the magnesium salt, and last 

 the salt of calcium should be added after having been dissolved by itself. By this 

 procedure only a small amount of insoluble calcium phosphate is formed. The 

 zoospores of Vaucheria may be induced to form at almost any time by transferring 

 this alga from the above solution, in which it has been growing exposed to a bright 

 light, to pure water; or cultures in a o.i per cent, or 0.2 per cent, nutrient solution 

 which have been exposed to the light need only be placed in a dark place in order 

 to incite the production of zoospores. 



A 2 per cent, to 4 per cent, solution of cane-sugar may be used as a nutrient 

 medium for algae. Filaments of spirogyra may be made to conjugate by trans- 

 ferring them from the water in which they have been growing to a solution of cane- 

 sugar as above, which is then placed in a well-lighted place. 



The formation of zoospores may be incited in cedogonium by transferring fila- 

 ments of the alga from water at a low temperature (say at the temperature of the 

 early morning) to a 2 per cent, or 3 per cent, solution of cane-sugar which is kept 

 at a constant temperature of about 26C. 



Convenient flasks for the preservation of sterilized fluid nutrient media may be 

 made from glass tubing as follows: A piece of glass tubing 0.2 inch in diameter, 

 or larger, is held with its lower end in the flame of a blow-pipe, the tube being con- 

 stantly revolved about its long axis to insure an even heating of the end of the tube 

 until the end of the tube becomes soft and just begins to draw downward in the 

 form of a large drop. By this time the mouth of the tube has become closed. 

 Then quickly the tube is removed from the flame, and while the melted end of the 

 tube is still held downward, air is blown in at the upper end of the tube by means 

 of the mouth, so that the molten glass at the lower end of the tube is forced out- 

 ward in the form of a rounded flask. After cooling so that it may be handled, the 

 tube is held in the flame close to the bulb, and by constant turning the tube is 

 heated equally on all sides until it becomes so soft that it may be drawn out. This 

 process is accomplished by taking the tube from the flame and pulling on it gently 

 so that it may be drawn out quite long and narrow. The length of the stem of 

 the bulb should be equal to the depth of the vessel from which the nutrient medium 

 is to be drawn into the bulb. The stem may be severed from the tube by holding 

 it in the flame of the blow-pipe at the proper distance from the bulb, where it will 

 soon become soft enough to be pulled off from the main tube. Then the end of 

 the capillary neck is held in the flame until a bead is formed; in this way the flask 

 is hermetically sealed. To fill the flask with nutrient fluid the neck is sterilized 

 near the end by passing it through a flame, and the head is broken off with sterilized 



