494 



SCIENCE. 



[X. S. Vol. XXI. Xo. 535. 



(4) Portland cement benclitops under in- 

 eubatoi-s and on other benches where gas 

 flames are in constant use. 



TJie Construction of a Thermostat-room: 

 N. MacL. Harris, University of Chicago. 

 Every well-appointed laboratory en- 

 gaged in teaching large classes should have 

 an incubator room. The costly copper 

 thermostat is entirely inadequate. The 

 thermostat in this case was built for the 

 pathological laboratory of the Johns Hop- 

 kins University and was modeled some- 

 what after one seen in JCjoebenhavn, Den- 

 mark, and one in the Institute for In- 

 fectious Diseases in Berlin. 



The cost of this room was one hundred 

 and twenty dollars exclusive of the thermo- 

 regulator and Koch safety burner, a sum 

 often exceeded by the larger sizes of the 

 ordinary copper-built apparatus on the 

 market. 



A complete description of this room will 

 soon appear in the Journal of Experi- 

 mental Medicine or in the Centralblatt 

 fiir Bakteriologie. 



The Utilization of Leaky Incuhators : C. F. 



Dawson, University of Florida. 



The leaky incubator is not an inicommon 

 piece of apparatus in the older laboratories. 

 Owing to the difficulty with which they are 

 kept in repair when once they have begun 

 to go to pieces, it is doubtful economy to 

 attempt, in most eases, to keep them in com- 

 mission. 



As ill the case of old and tried friends, 

 we dislike to part with them. Although 

 it is not the possession of such an incu- 

 bator, at present, that has prompted this 

 short note, a long laboratory experience 

 has shown me that many fine and expensive 

 old ovens liave been consigned to the worn- 

 out apparatus pile, because of their leaky 

 propensities. 



The writer is at present using one of 



Bausch and Lomb's finest incubators, with- 

 out the usual water-jacket, and has never 

 seen a more perfectly regulated apparatus. 

 In this case the mercury regulator is, of 

 course, passed through one of the tubula- 

 tures into the culture chamber. 



We thus directly regulate the amount of 

 heat in the place where it is wanted, and 

 not through the medium of heated water. 

 Such an apparatus is easily and quickly 

 regulated. There are no long periods of 

 over-heating or under-heating, as is the case 

 when we have a large volume of water to 

 heat up or to cool down. 



Some might object to the rapid cooling 

 when the door is opened ; but this is quickly 

 counteracted by an almost immediate re- 

 turn to the temperature for which the 

 regulator is set, when the door is closed 

 again. 



VCere this system adopted the expen- 

 sively constructed incubator would be a 

 thing of the past, as cheaper materials, 

 such as wood and tin, could be employed 

 in their manufacture. 



I., Demonstration of an Efficient Thermo- 

 h'egulator: A. Robin, Wilmington Water 

 Department Laboratory. 

 The thermostat consists of an ordinary 

 automatic gas burner, such as is sold in 

 hardware stores, connected with a regu- 

 lator made on the same principle as the 

 minimum and maximum thermometer with 

 three electrodes, one reaching 38° C, the 

 other 37° C, and a third connected at the 

 bend of the U tube. The spring wires 

 opening and closing the valve in the gas 

 burner are slightly bent so as to permit 

 a small amount of gas to pass, thus doing 

 away with the spark coil generally used to 

 light the burner. Two open-cell constant- 

 current batteries supply the necessary cur- 

 rent. When the temperature in the incu- 

 bator reaches 38° C. the mercury rises, 

 making a contact with the electrode on 



