INCUBATORS. 



79 



If the amount of gas which passes through the peephole is sufficient 

 still to raise the temperature of the chamber when c is closed by the 

 rise of the mercury, then the peephole is too large. Tube c must be 

 unshipped and e plastered over with sealing-wax, which is pricked, while 

 still soft, with a very fine needle. The gas flame, when only the 

 peephole is supplying gas, ought to be sufficiently large not to be 

 blown out by small currents of air. 



The varieties of incubators are, as we have said, 

 numerous. The most complicated and expensive are 

 made by German manufacturers. Many of these are 



FIG. 33. Hearson's incubator for use at 37 C. 



unsatisfactory. They easily get out of order and are 

 difficult to repair. We have found those of Hearson of 

 London extremely good, and in proportion to their size 

 much cheaper than the German articles. They are fitted 

 with an admirable regulator. It is preferable in using an 

 incubator to connect the regulator with the gas supply and 

 with the Bunsen by flexible metal tubing. It is necessary 

 to see that there is not too much evaporation from the 

 surface of cultures placed within incubators, otherwise they 

 may quickly dry up. It is thus advisable to raise the 



