338 



Kev. W. H. Dallinger on 



[May 2, 



Having, therefore, ultimately secured another sac, I determined to 

 use the -^g-th, as being, as I believed, the most suitable lens for the 

 purpose. In the still condition of the sac, ample time was given for 

 the most delicate adjustment of the light and of the lens, and the 

 watching was begun under the best conditions. 



Not the slightest movement, either within or without, is visible while 

 the cyst is in this condition ; and the time over which this inactivity 

 extended was never less than three hours, nor more than five hours, in 

 the eight separate instances which I studied. In the second instance 

 the length of time which elapsed was four hours. At the end of that 

 time, without reason discoverable at the moment, there was as before a 

 falling in of the centre of the cyst, and an irregularity in its shape, 

 with a visible and rapid diminution in size. At first nothing but a 

 cloudiness at the two ends could be discovered ; but, by a little delicate 

 adjustment of light and lens there became distinctly visible an outflow, 

 from the two ends and the middle of the cyst, of the most exquisitely 

 minute particles which I have ever seen ; and as the quantity flowing 

 out diminished, their segregation became more complete, and their 

 clearness and independence more manifest. 



The nature of the "continuous stage" — which keeps the drop of 

 fluid under examination from evaporating — is such as to compel the 

 use of the microscope in an upright condition, in order that the stage 

 of the instrument may be perfectly horizontal. On this account the 

 ordinary " camera lucida " is of no avail, or only of use by special and 

 difficult arrangements; but a beautiful little instrument, made by 

 M. Nachet, of Paris, specially meets this emergency, and enables us to 

 make camera lucida drawings with great ease and accuracy. I had, 

 therefore, by anticipation, arranged this apparatus : and when the out- 

 flow had continued for about five minutes, made a drawing of the cyst, 

 of which fig. 16, Plate 9, is an accurate copy. As, of course, the 

 minute particles were in rapid movement of outflow, they were put 

 into the drawing, not with camera lucida, but subsequently ; and they 

 accurately represent what was seen at the time. The emission con- 

 tinued for about forty minutes, becoming more and more feeble, until 

 at last there was no more movement. At this stage there were many 

 of these minute particles well segregated round the ends of what re- 

 mained of the cyst; and then I was able, not only to make a drawing 

 of the delicate white film of the cyst, but to indicate by fine dots the 

 relative appearance of the cyst and the still particles. This drawing 

 is reproduced at fig. 17. 



The entire details of the subsequent history of these minute bodies 

 were of course only made out by several successive and continuous 

 observations on the emissions of different cysts. But, in each case, 

 the lens was fixed upon some of the minute bodies that remained 

 near the exhausted cyst, and then the observation was unbroken 



