258 THE NORTHERN MICROSCOPIST. 



and acute contagium bacteria, pleomorphy, and a definite alterna- 
tion of generations occur in the history and development, which is 
the same for all these species, though the bacterium in each disease, 
as also in typhoid, is perfectly distinct. The size, colour, habits, 
movements and metastasis, together with the general conditions of 
their existence, serve to distinguish the different species. 
FLuip FOR HoMoGENEOuS IMMERSION.—Some recent experi- 
ments of Prof. Abbé (see Bot. Centralbl. x. (1882) pp. 224-5) 
with pure cedar oil have resulted in the formation of a fluid which 
Dr. L. Dippel considers perfect for its purpose. The pure oil is 
: spread out so as to present as large a surface as possible to the 
action of the light and air. When thus treated, it gains the consist- 
ency of castor-oil, and while its refractive index is raised to 1.518- 
20 it undergoes no increase in dispersive power. ‘The refractive 
index can be reduced if desired by adding olive or castor oil. 

CHEMICAL DIFFERENCE BETWEEN DEAD AND LivING Proro- 
PLASM.—Dr. O. Loew is still working at this point, and has executed 
photographs to shew the difference between the action of dead and 
living cells upon a weak solution of silver nitrate. It will be 
remembered, perhaps, that some time ago he elaborated a theory 
according to which protoplasm consists of certain aldehydes, and 
its life depends upon the possibility of inter-molecular action 
between them. Some of the experiments made for the purpose of 
establishing the theory were extremely interesting. ‘The filamentous 
Alge, Spirogyra and Zygnema, after twelve hours immersion in a 
solution of silver nitrate, of one part in a hundred thousand, were 
. black with the reduced silver. Algze killed before immersion give 
; no trace of the reaction. It was found that the Alge survived a 
. temperature of 35°C, but not 50°C. Immersion in solutions of 
. veratrin and acetate of quinine did not destroy the reducing power 
of the filaments. ‘The experiments were not confined to Algz, but 
extended to other plants. Cladophora, the Moulds, Schizomycetes, 
the Diatomacez, and others, gave results generally resembling one 
another but differing in detail. The reducing properties above 
described are shared by the highly organised vegetable tissues, and 
| in some instances—as with a few of the Infusoria—by animals. 
Makinc Drawincs or Microscopic Onjects.—But it will pro- 
bably be asked why I did not kill my object before drawing it? I 
answer that I could never make a drawing to my mind from a dead 
aquatic larva or insect . . . to say nothing of the fact that a 
dead aquatic insect so loses the peculiar distinctive character de- 
rived from its favourite attitude and position, that though the 

