700 MICROSCOPY. 
slide they seldom revive; because they crawl about until the last 
moment, and thus part with so much of their protective covering 
that they are finally dried up and destroyed. 
Notwithstanding the first impression of some of the Fellows of 
the Society, that Mr. Davis’ researches had been entirely antici- 
pated by many continental authorities, the doctrine of the gelati- 
nous envelope seems to be an entirely original as well as a very 
satisfactory settlement of a much disputed question. 
Action or Poisons oN THE BLoop Corpuscies.— Dr. Osler 
read a paper before the Medical Microscopical Society, in London, 
giving the results of his experiments on the action of solutions of 
the sulphates of atropa and of physostegia upon the blood corpus- 
cles. He hoped to show, in the corpuscles, the already demon- 
strated antagonism between these reagents, but reached an exactly 
opposite result, both solutions checking in a somewhat similar 
manner the amceboid movements of the white corpuscles, and both 
causing the red corpuscles to become irregular from involutions 
and cuppings of the surface. The reagents mixed produced the 
same changes as when separately applied. Solutions of curare 
were also mixed with blood, but produced no positive results. 
Limrr or Resotvinc Power. — How little we appreciate the 
extent to which the resolving power of our best objectives falls 
below the possibilities of their amplifying power, was well illus- 
trated by the surprise of many microscopists, and the incredulity 
of some, when Nobert’s 19th band, of 112,000 lines to the inch, 
was beautifully resolved by a power of scarcely over two hundred 
diameters ; while, with absolutely faultless definition, the same lines 
ought to be visible undera much lower power than that. What 
we ought, theoretically, to be able to see with powers of from one 
to three thousand diameters, is computed in the following curious 
extract from one of Dr. Pigott’s recent papers. 
“ With regard to these minute quantities [beading one hundred 
thousandth of an inch in diameter, etc.], and to remove doubts 
which may arise in some persons’ minds as to the possibility of 
seeing such very minute linear quantities, I may say that a minute 
of are corresponds to the breadth of the 334th part of an inch as 
seen at ten inches, which is at least four times as thick as 4 human 
hair at that distance. Now the one hundred thousandth of an 
nch under a power of 1,000 is precisely the same thing as a thous- 
