MICHIGAN ACADK.MV OF SCIENCE. 303 



Effect of Dry Heat: 



In ordei' to determine the effect of dry heat a large test tube was used, 

 with a tliermometer inserted through a rubber stopper so th.it the bulb 

 was suspended about 5 mm. above the bottom. Tlie tube was heated in 

 tlie water bath until the air within reached the desired temperature as 

 was indicated by the thermometer. Three cover slips upon which a dro]) 

 of spore suspension had been previously placed and dried over CaCl.,, 

 were dropped into the tube and were held at the constant tempc-rature 

 for 10 minutes. It was found that tlie sjiorcs survived cvrn when lieated 

 at 75 °C., for 10 minutes. 



Thermal death-point of the Germinated Spores: 



Spores in the process of germination are known to be more sensitive 

 to high temperatures than ungerminated spores, because of their weak- 

 ened condition. This is the principle involved in the Tyndal method of 

 fractional sterilization. 



Clover juice cultures 31 hours old were heated (in triplicate) for 10 

 minutes in the manner before described. An additional thermometer 

 immersed in the tube of clover juice was kept in the basket along with 

 each set of culture tubes, and the time required to raise their temperature 

 from tliat of the room to that of the bath, determined. This varied from 

 two to two and one-half minutes and was not considered. After heating, 

 the tubes were immediately cooled by plunging into ice water. The 

 thermal death-point of these germinated spores was found to lie between 

 15 and 18^°C. for 10 minutes. Within 34 hours, it is quite certain that 

 all of the viable spores had germinated, thus eliminating the possibility 

 of growth, after heating, of any ungerminated spores. In the check 

 experiment it was found that ungerminated spores heated in clover juice 

 at 481/2 °C. were not killed even after an hour's exposure. 



RELATION OF HUMIDITY TO GERMINATION. 



Lesage, (1895), gives a method for determining the minimum humidity 

 requirements for the germination of the spores of Penicilliinji glaucum. 

 This method has a wide adaptibility, and should prove valuable in deal- 

 ing with parasitic fungi. A similar method was used for determining 

 the humidit}' requirements of Macros poriiim sarcinaeformc. 



The principle involved is that tlie saturation of air above a given solu- 

 tion varies inversely as the concentration of the salts dissolve therein. 

 For NaCl the formula 



1 — n a 



was deduced, where 1 equals 100% of saturation, n the number of grams 

 of salt, dissolved in 100 cc. of water, and a is a constant, which for 



