232 THE MICROSCOPICAL NEWS. 
the basis of reasoning established here, which depends on the con- 
dition of a constant visual angle of the inherent dissipation of the 
rays for different distances of the objective-image. This condition 
(as has been observed) holds good with sufficient approximation 
only as long as that distance—the length of the microscopic-tube 
practically—is not foo small a multiple of the focal length of the 
objective ; this is zo¢ fulfilled, under ordinary circumstances, with 
the very low-power systems which would come in question for 
apertures of only a few degrees. 
4. The values of v assigned above for different kinds of 
objectives express, in my opinion, the conditions of the dest possible 
performance of the microscope under present circumstances. I 
by no means contend, however, that much higher super-amplifica- 
tions might not still be very useful ; but if it cannot be denied that 
with the objectives which are made at this date, a defter image is 
obtained under a four-fold, or six-fold, super-amplification than can 
be obtained under a higher figure, it is absolutely certain that the 
lower powers ought to be used, when the wtmost attainable degree 
of perfection is required. It is quite immaterial for that conclusion, 
whether the loss of sharpness (‘“‘ definition ”) attendant upon higher 
values of v, may be deemed small or great, and whether it may 
become obvious with all preparations or with a few only. If there 
zs a loss, however small, and if only ove kind of object is found 
‘with which it can be perceived, this alone will be sufficient to prove 
the advantage of the lower numbers ; for there cannot be a reason- 
able doubt, that even the slightest difference in the perfection of 
the microscopic image may become a matter of decisive importance 
in critical cases of difficult research. 
( Zo be continued. ) 
BACTERIA OF THE CATTLE DISTEMPER.* 
HE bacterium of the cattle-distemper has been hitherto known 
almost exclusively in the bacillus condition, not making its 
appearance in the blood till some ten hours before the death of the 
animal. F. Roloff has examined the blood in the early stages of 
the disease, and also those organs, especially the spleen and the 
lymphatic glands, in which the bacilli are first seen. In all these 
he found a large number of small round shining bodies of micro- 
cocci. The infection of other animals with blood containing these 
cocci, produced in them the ordinary distemper with its bacilli, 
showing that the two are stages of development of the same 
organism.—/. R. M.S. 
* Arch. Wiss. u. Prakt. Thierheilkunde, ix. (1883). See Bot. Centralbl., xvii. 
(1884) p, 112, 
