The President's Address. Btj the Rev. W. H. DalUnger. 195 



being racked up and down by a milled head. We thus control the heat 

 accurately. The flames should be guarded by small glass cylinders. 

 Moreover, for low temperatures it is needful to be able to control the 

 amount of gas which shall be the minimum amount when the mercury 

 has risen to block out the main supply ; this I have accomplished by 

 means of a collar of diaphragms seen in figs. 32 and 33. In A the end 

 of the glass tube bringing the gas into the instrument is 

 shown, viz. of fig. 31. C of fig. 32 is the platinum ^^' ' ^^"' ^ " 

 tube which makes contact with the mercury ; it is best 

 for its end to be at an angle ; it cuts the gas off more 

 gradually. E is the aperture through which gas goes 

 out when the tube is blocked with mercury. Now it 

 is needful to have the amount of this under control. 

 This is done by a collar of diaphragms, seen at F in B, 

 fig. 33, which is placed upon the platinum tube D. There are different 

 sized apertures in this collar, as G, H, I, and the hole E in A being 

 made as large as the largest in the collar, and the collar revolving gas- 

 tight, we can use at will a larger or a smaller aperture. 



By a simple arrangement, which I have already for another purpose 

 exhibited and explained to this Society,* I constructed a warm stage 

 fitted to a suitable Microscope, which was attached to the large water 

 vessel of the thermostat, by tubes, so that the water in the vessel was 

 kept in constant circulation in the stage, and by this means I could 

 examine the organisms in the glass vessels at the temperature at which 

 they were living. 



I confined my attention to three well-known organisms, whose life- 

 cycles I fully understood, and had completely followed. They were 

 those which Mr. Saville Kent has named Tetramitus rostratus, Monas 

 Ballingeri, and D. JDrysdali. Of course, beyond these there were a large 

 number of putrefactive forms in great abundance, such as Bacterium 

 termo, B. lineola, Spirillum volutans, and other forms of monads. But 

 my attention was confined wholly to the three specified organisms. 



I resolved on using very minute increments of heat very slowly. 

 I commenced at a normal temperature of 60° Fahr., and the first 

 four months were employed in raising the temperature 10°. This, 

 by control experiments, I found to be quite unnecessary in itself, for 

 even a relatively very rapid rise from 60° to 70° Fahr. will quicken the 

 multiplying power of these organisms. 



But also, by rough control experiments, I learned that the more 

 slowly and regularly the first increments of heat, between 60° and 70°, 

 were superimposed, the greater safety was there in slow progressive 

 advance. 



But no discoverable change took place during this time. The 

 normal processes went on in a normal way. The organisms were 

 extremely abundant; fission occupied the same time, and occurred at 

 the same intervals ; while the spore-sacs, resulting from the blending of 

 two forms, were as we have always seen and described them. 



At every successive access of heat I made very critical examinations, 

 not only of the morphological details, but also of the condition of the 



* Cf. infra, p. 317. 



