17 



II. — Note on a New Growing Cell for Critical Observations 

 under the Highest Powers. 



By A. A. C. Eliot Merlin. 



(Read November 18, 1908.) 



Having at various times done a considerable amount of high -power 

 work on living bacteria and the smaller monad forms, it was found 

 that for critical observational purposes, under even oil-immersion 

 objectives, a well-constructed Rousselet live-box as usually made 

 afforded perfectly satisfactory results except that the thin water 

 film containing the specimens was certain to quickly evaporate, so 

 that in the hot summer months any individual organism could 

 only be studied for about half an hour. To obviate this very 

 serious drawback, a modified live-box was made for, ami described 

 by me,* in which evaporation was retarded by means of an india- 

 rubber band placed round the rim. 



I now venture to bring to your notice an improved form of 

 moist and warm chamber box which has been found in practice to 

 work most satisfactorily, a very small and excessively thin film 

 having remained unaffected by evaporation during three weeks in 

 the hottest summer weather, the thermometer standing at well 

 over 80° F. 



The accompanying illustration (fig. 1) will explain the design 

 of this little piece of apparatus more clearly than any verbal 

 description, the appliance consisting of a closed rectangular warm- 

 water circulating tank 3*5 in. long, 2 in. wide, and 0*G in. deep. 

 In the centre there is a circular well 1 ' 6 in. in diameter, with a 

 glass tablet, • 4 in. in diameter, mounted flush with the under 

 surface of the tank. The cover- glass carrier is as in the liousselet 

 model, except that it is provided with a flange, 0*3 in. broad, 

 which rests on another flange on the upper surface of the rect- 

 angular tank, so that when the | in. cover is in position close 

 over the tablet, f there is just space for a ring of thick blotting paper 

 or linen to lie in position between the flanges. The blotting paper 



* Journ. Quekett Micr. Club, series 2, ix. (1905), p. 169. 



t Although this contrivance is more especially designed and intended for the 

 observation of small monad forms under high powers, for which a very thin water 

 film is desirable, it will be found that, by placing two or more blotting-paper 

 rings between the flanges, the depth of the cell can be suffL d to 



accommodate the larger organisms, such as rotifers, etc., without subjecting them 

 to injurious pressure. 



Feb. 17th, 1909 r 



