60 MEDICAL MYCOLOGY 



the bottom of the cell prevents drymg out, since its vapor pressure is prac- 

 tically the same as that of the hanging drop. The cell may be placed on the 

 stage of a microscope and studied from time to time until the nutrient material 

 in the drop is exhausted. One should be careful not to have the drop too 

 large, since it will be difficult to focus to the bottom of it if the spore under 

 observation should not be thoroughly wetted and lies in the surface layer of 

 the drop, or is so heavy that it falls to the bottom of the drop. To avoid this, 

 sometimes a thin film of agar is used instead of a liquid drop, in which case 

 distilled water is usually placed in the bottom of the cell to prevent drying 

 out. Sometimes a very young colony with a small amount of the surround- 

 ing agar is cut out and placed on the cover glass, making a hanging block 

 culture described by various authors including Dalmau (1929-1930). Studies 

 made by these methods are especially valuable in following the early stages 

 in the development of a spore or in the evolution of the life cycle. Various 

 types of hollow-ground slides, etc., have been developed, but for convenience 

 and general use, they have little advantage over an ordinary Van Tieghem cell. 



Giant Cultures. — At the other extreme from the microculture, we may use 

 giant cultures. These colonies which are allowed to develop over a long 

 period on an abundant supply of substrate, are very useful in giving gross 

 morphology on various media and often are strikingly characteristic in ap- 

 pearance for different species. They have had little favor in most labora- 

 tories, as they must be allowed to grow from one month to two or three before 

 this character can be ascertained. However, they have been utilized with very 

 excellent results by Sabouraud and others in the dermatophytes and by Lindner 

 in the yeasts. Since, under ordinary conditions a Petri dish is too shallow to 

 hold sufficient medium, and allows it to dry out too readily and also to be 

 subject to contamination, various specialized culture dishes have been devised. 

 Perhaps the Roux flask, of which there are several types on the market, is the 

 best known, although somewhat expensive. Ordinary cultures in Erlenmeyer 

 flasks are satisfactory for most purposes, but they do not admit of either 

 microscopic examination or photography without breaking the flask, which 

 is frequently difficult to do without injury to the colony. To obviate this for 

 photographic purposes, Shrewsbury (1931) suggests growing them in green 

 glass medicine bottles of 10-12-ounce capacity (with flat sides if possible). 

 The bottle may be evenly broken by application of a red hot nail along the 

 sides. These bottles are also useful for growing cultures under diminished 

 pressure since the glass is strong enough to resist almost complete exhaustion. 

 He also suggests their use in exposing the inverted colony to fumes of various 

 antiseptics, such as ethyl iodide. 



Karrenberg has suggested two ingenious devices which permit giant 

 colonies to be photographed or studied with the low power of the microscope 

 with a minimum chance for contamination. In 1926 he suggested an inner 

 test tube carrying an agar slant from which the side had been removed. This 

 was stored in a somewhat larger test tube plugged with cotton. When it is 

 desired to photograph or to examine the colony, the inner tube may be easily 



