132 
PROGRESS OF MICROSCOPICAL SCIENCE. 
number of tlie £ American Journal of Science,’ to which we refer our 
readers for more details. The stages are all those after the lobster has 
left the egg, as those within the ovum are well known already. The 
author, Mr. S. J. Smith, makes four stages in the post-ovum develop- 
ment of this animal. These he then minutely describes and figures, 
and he considers that the fourth is the adult stage. He thinks, too, 
that there is probably another stage between the third and fourth. 
A Microscopical Examination of the Skin in Impetigo contagiosa . — 
An interesting paper on this subject appears from the pen of Dr. H. 
G. Piffard in the ‘New York Medical Journal,’ June, 1872. The 
author says that the first examination was made March 7th. By this 
time the potash had effected an almost complete solution of the crusts, 
with the exception of a few small, whitish masses, which remained un- 
dissolved. One of these was transferred to a glass slide, a little gly- 
cerine added, and a thin covering glass applied. Upon examination 
with a ^ (Grunow) little was found to attract attention except a few 
collections of very transparent epidermis, without visible nuclei, many 
oil-globules, and some granular matter. The first half-hour yielded, 
with the exception of the above, but negative results. At this time a 
slight modification of the method of illumination brought to view a 
minute circular body whose exceeding transparency had hitherto ren- 
dered it difficult of detection. Applying a higher power (-^g- Grunow), 
and carefully focussing, the body exhibited a peculiarity of form which 
was exceedingly striking. The effect produced by depressing the 
objective was similar to that with which we are all familiar in the case 
of the red blood corpuscle, namely, the border first came into focus, as 
evidenced by the bright outline and dark centre, and then, upon 
further depression, the border became dark and the centre brighter. 
Iieversal of the movement produced a reversed effect. The first im- 
pression was, that the body under examination was in reality a blood 
corpuscle, so thoroughly was its appearance counterfeited ; but its 
minute size, and the fact that it had lain two days in a potash solu- 
tion, precluded this possibility. Further search detected six or seven 
similar bodies in the same field, and prolonged examination of the 
preparation, and of others upon succeeding days, enabled me to deter- 
mine the few following facts The bodies, which were unquestionably 
vegetable organisms, were generally circular in outline, a few being 
oval. Their average diameter was sisoo °f an inch. Their form, as 
determined by focussing, appeared to be the same as that of the red 
blood corpuscle, namely, a biconcave disk. The spores were usually 
isolated, but occasionally two or three, and in one instance four, were 
found together. In this latter case, three of them were circular, while 
the terminal at one extremity of the chain was oval. In another case 
the two-days-old crust was placed in a three-per-cent, solution of 
potassa fusa, while a small fragment of the older crust was macerated 
for a few minutes in a mixture of liquor potassse and glycerine, and 
immediately examined with a T h-incli objective (Wales). The field 
presented was extremely striking. Not only were the Memo-discoid 
bodies, which wo had previously encountered, present in abundance, 
but others exhibiting an almost endless variety of form. This unex- 
