84 A MANUAL OF BACTERIOLOGY 



either by a sliding tube, in Page's, or by a screw, in 

 Reichert's, so that the temperature may be set at any 

 desired point. In this country Hear son's incubators are 

 now generally employed (Fig. 13). In these the regulator 

 consists of a capsule containing a fluid of a certain boiling- 

 point, which when ebullition takes place raises a lever 

 and so partially cuts off the gas supply. While the 

 Hearson regulator is a very constant one, it has the 

 disadvantage that it can only be used for a range of 

 temperature of a few degrees unless the capsule be changed. 

 The Hearson incubators are heated with gas, oil, or 

 electricity. At least one incubator is required, and it is 

 convenient to have two or three. If there be only one 

 the regulator should be set for a temperature of 37 C. ; 

 if more, another should be kept at about 20 C. The 

 incubator at 37 C. is termed the warm or blood-heat, 

 and that at 20 C. the cool or room temperature one. 

 A warm room or cupboard will serve most of the purposes 

 of the cool incubator. A third incubator set for 25 C. 

 is useful for fermentation work. For maintaining the 

 cool incubator at 20 C. in summer or in a hot climate a 

 form of Hearson incubator has been devised in which a 

 stream of cold or iced water runs through the jacket. 



A substitute for the large and expensive incubator can 

 readily be devised. An ordinary chemical hot-water oven 

 may be employed, or simply a smaller tin set in a some- 

 what larger one, the interspace being filled with water ; 

 and, with a little scheming, regulators can be dispensed 

 with by making use of a small gas or lamp flame/varying 

 its size and distance from the bottom until the right 

 temperature has been attained. A Thermos flask, or a 

 Dewar's vacuum flask, or the writer's Milk Pasteuriser 

 (made by Messrs. Allen and Hanbury) filled with water at 

 the proper temperature may be utilised as small incubators. 



Gelatin will remain solid only at temperatures below 



