INCUBATORS 1 5 



while a streptococcus slant would have almost five. It has been estimated that such 

 a standard loop would contain between 2,000,000,000 and 3,000,000,000 organisms. 

 Of the greatest use in culturing material obtained at autopsy is the platinum spud. 

 This can be made by hammering out one end of a piece of 15- to i8-gauge platinum 

 wire. 



For making smears from faeces, sputum, and the like, wooden tooth- 

 picks are very convenient; the kind with the spatulate end is preferable. 



Incubators. When gas is obtainable, the maintaining of a constant temperature 

 for the body temperature incubator (38C.) and the paraffin oven (6oC.) is best 

 secured by the use of some of the various types of thermo-regulators. The Reichert 

 type is the one in general use, although there are many features about the Dunham 

 and Roux regulators which are advantageous. 



If the pressure of the gas-supply varies from time to time, it is essential to regulate 

 this by the use of a gas-pressure regulator (MurrilPs is a cheap and satisfactory 

 one). 



Incubators, controlled electrically, can be obtained of certain foreign makers, and 

 are quoted in catalogues of American dealers. It is probable that the Koch petro- 

 leum lamp incubator is the most satisfactory one where gas is not obtainable. 

 They should be of all metal construction, and not with a wood casing, on account of 

 the danger from fire. They cost from twenty-five to fifty dollars. 



An incubator may be extemporized by putting the bulb of an incandescent electric 

 lamp in a vessel of water. The proper temperature may be obtained by increasing 

 the amount of water or by covering the opening more or less completely with a towel. 

 The test-tubes to be incubated can be put into a fruit jar or tin can, which receptacle 

 is placed in the vessel heated by the lamp. 



Emery suggests the use of a Thermos bottle as an incubator. 



The vacuum bottle should be first warmed by pouring in warm water. After- 

 ward the bottle should be three-fourths filled with water at iooF. 



Schrup suspends his cultures and thermometer in the water by threads attached 

 to pins in the cork of the vacuum bottle. The plug should be paraffined or covered 

 with a rubber cap. As regards the matter of a low-temperature incubator (for 

 gelatin work), this may be met by using a small refrigerator. The ice in the upper 

 part maintains an even cold, and by connecting up an electric lamp in the lower part 

 of the refrigerator we can easily maintain a temperature which only varies one or two 

 degrees during the twenty-four hours. The gelatin plates or tubes should be placed 

 on the shelves usually provided with the refrigerator and not on the bottom. 



With a i6-candle-power lamp a temperature of about 2SC. is maintained (this is 

 too high, being about the melting-point of gelatin); with an 8-candle-power, one 

 about 21 to 23C.; and with a 4-candle-power, from 18 to 2oC.; the box being 

 about 20X30X36 inches. 



More recently we have used with entire satisfaction a low tempera- 

 ture incubator made by Hearson. 



The low temperature is supplied by water from cracked ice packed in a large cen- 

 tral chamber. A small dynamo controlled by a thermostat circulates the water 



