ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



317 



Dr. Dallinger's Thermostatic continuous Stage is constructed on the same 

 principle as the preceding. It was devised for the continuous observation 

 under high powers of the minutest living organisms, and was used by Dr. 

 Dallinger and Dr. Drysdale for the continuous watching of monads as 

 described in ' The Monthly Microscopical Journal,' 1869, pp. 97 et seq. 

 The primary object was to arrange the field of observation, consisting of a 

 minute drop of a septic fluid containing a given organism under observa- 

 tion, so that it might be observed with the highest powers, uninterruptedly, 

 and yet that the drop of fluid should not be suffered to evaporate. The 

 details of explanation as to how this was accomplished are given in the 

 paper above referred to. It will suffice here to point out that the non- 

 evaporation was accomplished by causing the objective and the covered drop 

 to work in an air-tight chamber kept by capillary action constantly so 

 saturated with aqueous vapour that the air within that chamber had, as it 

 were, no room to receive the vapour from the covered drop on which 

 observations were being made. 



The present piece of apparatus aims at precisely the same thing, with 

 the additional aim that the covered drop and all surrounding it shall be, 

 and shall be static at, any temperature required. It was employed specially 

 to investigate the life-history of a septic organism whose normal fluid was 

 from 90° to 95° F. 



The stage was made as described in the above paper, but it was made 

 hollow and water-tight. The whole stage is seen in perspective in fig. 81. 



Fig. 81. 





[B 



At A, a 6 are two grooved pieces of solid metal which permit the stage to 

 slide on to the stage of an ordinary Microscope and partake of the mecha- 

 nical movements elfected by the milled heads. 



B is a vessel for v^ater with a thermometer a of sufficient delicacy 

 for indicating the temperature. & is a mercurial regulator, carefully made, 

 but of the usual pattern ; c brings the gas from the main ; d conveys as 



