CULTIVATION AND EXAMINATION 47 



tures of 24° to 25° C, although wholly typical cultures are produced at 

 both temperature levels. 



In the production of spores for biochemical investigation (see p. 37) and 

 in the conduct of such studies themselves, temperature is often very im- 

 portant. In work of this kind, it is essential to determine the optimum 

 temperature for each organism and process, and then to control this within 

 a narrow range in order to secure consistent and reproducible results. 



Temperature is known to be a critical or limiting factor only in a few 

 species, but its effect in these is sufficiently pronounced that its influence 

 should not be disregarded in any case. 



CULTURE TOOLS AND EQUIPMENT 



Transfer Needles 



In making transfers, we have used with satisfaction for many years a 

 Xo. 20 or No. 22 B. and S. gauge nichrome wire thrust into a slender brass 

 or stainless steel tube so that only about 15 to 20 mm. are exposed. (The 

 tubing employed is of the type used in temperature controls of mechanical 

 refrigerators and other thermostatically controlled devices.) The point of 

 this wire is then ground down to the sharpness and smoothness of a needle. 

 This instrument can be heated to redness in the flame a great many times 

 with only the occasional necessity of resharpening. It thus has many ad- 

 vantages beside cheapness: it is firmer and takes a better point than plati- 

 num; it withstands sterilization in the flame, which promptly destroys the 

 usefulness of steel ; and it can be made any size or length to suit the work- 

 man's purposes or preferences. 



Loops 



Loops of various dimensions are very useful and can be inserted into 

 handles made from small brass or stainless steel tubing as noted above. 

 These, too, can be fashioned from nichrome wire, but it has been our 

 experience that loops made of platinum-iridium wire possets certain marked 

 advantages. While these are not as rigid as nichrome loops, they are much 

 more rigid than loops of pure platinum, and they can be re-heated indefi- 

 nitely without corroding. Loops of this type will be found especially 

 useful in making mass inoculations, such as the seeding of large tubes and 

 plates for the production of spores to be used in various types of experi- 

 mental work. 



Mounting Fluid 



In the microscopic examination of the Aspergilli it is often satisfactory 

 to mount conidia, heads, or other structures in water. It is more generally 



