Report OH the Bacteriology of Water. 



327 



The following set of experimental observations were made to test 

 more accurately the heating of the cells, and the rise of tempera- 

 ture in the cultures, as compared with the temperature of the thermo- 

 meter merely between the glasses, and that in the air close to the 

 culture. 



One of my moist chambers was prepared exactly as for a culture, 

 except that one of the two arms was cut short so that the bulb of a 

 thermometer could be inserted into the cavity as shown in the accom- 

 panying figure. 



8, 





J 



a = cavity of the glass cell (moist chamber) the atmosphere in which is kept 

 saturated by water-vapour which evaporates from the layer of water b and wet 

 cotton-wool plugs c and c'. d the hanging-drop suspended from the cover-slip. 

 The latter is luted to the glass-cell by stiff gelatine ; while the floor of the cell is 

 formed by a glass slide (e) cemented by paraffin melting between 55 and 60 C. 



At c' the second open arm of the glass cell has been cut short to receive the bulb 

 of the thermometer f (the bulb of which may be blackened), g and g' are the 

 coloured glasses, so placed that all the light reaching the hanging-drop d must pass 

 through them. 



Having arranged such a cell over the mirror of the microscope, and 

 loaded another microscope with an exactly similar thermometer 

 whose bulb (blackened or not as necessary) is merely suspended 

 between glasses similar to g and g', I proceeded to compare the 

 temperatures on a hot bright morning, at a south window, with those 

 registered by thermometers hanging from the microscopes, and lying 

 on the table at the base. 



In the following table, the records of the thermometers outside the 

 microscopes are given in the first column ; those whose bulb was 

 merely supported between the coloured glasses in the second (under 

 the heading " dummy ") ; and that whose bulb was in the culture cell 

 under the third column. The bulbs in second and third columns were 

 blackened, the others not. 



