SLIDE CULTURES 69 



may be easily made with most molds by growing them directly on 

 slides or cover glasses. 



Slide Cultures. Slide cultures may be made either with solid or 

 liquid media. It is best to have the medium not too rich in nutri- 

 ents, since then the mycelium becomes rather densely packed and 

 it is difficult to make out details of structure. The agar should be 

 as clear as possible, because the presence of precipitates obscures 

 the field. Since only small amounts are required, it is quite practical 

 to filter the agar through paper. The slides or cover glasses used 

 must be clean and free from grease, so that the medium will spread 

 in a thin, uniform film. They may be kept in the usual acetic acid- 

 alcohol mixture until used. 



A convenient culture chamber may be prepared by placing in a 

 Petri dish a piece of glass tubing bent to a V shape. A glass slide 

 is laid across this and the dish, slide, and supporting tubing are 

 sterilized in an autoclave. If, during sterilization, the slide has fallen 

 off its support it can be replaced with sterile forceps. Melted agar 

 is then placed on the slide at a sufficiently high temperature and in 

 sufficient amount to cover with a thin flat layer of agar an area about 

 half the length of the slide and three-fourths its width. When the 

 agar has solidified, the fungus should be planted by streaking spores 

 in two parallel rows extending the length of the agar. Water should 

 then be placed in the bottom of the dish. Distilled water will pro- 

 vide a very humid atmosphere. By the addition of small amounts 

 of salt to the water, various degrees of humidity can be maintained. 



When the fungus has reached the proper stage of development it 

 can be examined under the microscope. For the study of fine de- 

 tails it must, of course, be covered. If the fungus to be examined 

 is a dry mold it must first be wetted. The slide is held by one end 

 and absolute alcohol is dropped at the upper end of the culture. 

 When it has drained off, the bottom and edges of the slide are wiped 

 with blotting paper and the slide is placed on the table. Then 2 or 

 3 drops of 10 per cent sodium hydroxide or other mounting fluid is 

 placed upon the culture and a large cover slip is carefully placed 

 over it. The preparation is not permanent but is excellent for exam- 

 ination and photography of the unshrunken mycelium, conidiophores, 

 and spores, and will keep for a few days. Because of the danger 

 of scattering spores this method is not suitable for use in the exam- 

 ination of some fungi pathogenic for man. 



Cover glasses require less space for incubation than slides, and a 

 number of cover glasses can be incubated readily in a Petri dish. 

 Stained cover glasses can be mounted in balsam to make permanent 



