74 
The Presidenfs Address. 
of the most interesting sights I ever witnessed was the evolu- 
tions of a living mucus-corpuscle^ obtained from the saliva. 
The rapidly moving particles within the corpuscle were dis- 
tinctly seen ; after a little while the outline of the corpuscle 
was subject to frequent changes_, bulging out first at one 
point and then at another^ and the moving particles freely 
entering and returning from these projections : these move- 
ments might be compared with the convulsive throes of par- 
turition of the higher organisms. After a time a large pro- 
jection was formed at one side^ and as this increased^ the 
outline of the corpuscle became regular and quiescent. 
Presently an indentation appeared between the corpuscle and 
its offset, and, no doubt, had time permitted, the complete 
separation of the young corpuscle from its parent would have 
been observed. 
I must, in conclusion, remark that I have not hitherto 
succeeded in developing any point of organic structure with 
Powell's Vt*^ that is not equally visible with a tV^^ ^7 
Ross ; further observation may, however, serve to elucidate 
points of evident advantage in the deeper power. It must 
be observed, that the inrth does not work well with thicker 
covering-glass than '0035 ; and in order to allow for some 
little distance of the object below the covering-glass, it is 
better to use '003. The -nrth employed was originally cor- 
rected for covering-glass of ordinary thickness, say -006 to 
•007, and could not be adequately corrected by separation of 
the anterior combination for glass only '003 inch thick. In 
order to compare the objectives on the same objects, it 
therefore became necessary to construct a new anterior 
combination for the tV'*^^^ specially adapted to very thin 
covering-glasses ; and it now works as correctly with these, 
as it does with the original combination, under the conditions 
which that was designed to fulfil. 
