2 THE MICROSCOPICAL NEWS. 
age of givirly transparency to the protoplasm and the cell-walls, but 
has also the inconvenience of destroying the protoplasm after some 
hours. Strasburger has nevertheless used it in his observations on 
the division of nuclei. He placed the plants in water containing 
1-50oth of sugar, and added one or two drops of a 1 per cent. 
solution of osmic acid. 
Vignal* and Cortest have called the attention of naturalists to 
the good results obtained with osmic acid for fixing instantaneously 
the forms of the lower organisms (/Vocts/uce, infusoria, algze, zoo0- 
spores, microbes of virulent diseases, &c.) Generally it is sufficient 
to expose the organisms on the slide for fiye minutes to the vapours 
of a 1 per cent. solution of osmic acid. But if they are very con- 
tractile it is preferable to treat them directly with the liquid acid 
after all disturbance of the slide has ceased. 
Certest has succeeded in doing away with the corrosive action of 
osmic acid. He places the organisms to be examined in a test-tube 
containing 30 c.cm. of distilled water or a few drops of the water of 
which he intends to make a microscopical analysis. He adds to it 
1 c.cm. of half per cent. osmic acid. Ina few minutes he fills up 
the test-tube with water, and allows it to rest for twenty-four or even 
forty-eight hours. All the algze, spores, bacteria, monads, vibriones, 
amcebz, and infusoria which originally swarm in the water are then 
deposited at the bottom of the test-tube. They are collected by 
means of a pipette, after the greater portion of the liquid has been 
decanted. 
For eleven months we have preserved, in the same test-tube in 
which they were killed, some specimens of J/onas which, during life, 
were very active. Their form has hitherto undergone no alteration. 
It is exactly the same as at the moment when they were attacked 
by the osmic acid. 
Taking our stand on the fixative properties of this agent, we have 
attempted to make use of it to determine the parts of an organism 
endowed with spontaneous motility. We had to decide whether the 
long caudal filaments, the existence of which we had recognized in 
the Bacterium rubescens of Ray Lankester, are contractile, and whe- 
ther they are active or passive in locomotion. 
With this object we poured into two watch-glasses some distilled 
water, and a few drops of the water in which they were multiplying 
abundantly. We added to the contents of one of the two watch- 
* “ Recherches histologiques et physiologiques sur les Noctiluques,” Arch de 
Physiol., 1878. 
+ “Sur une méthode de conservation des infusoires.” Comptes Rendus, 3rd 
March, 1879. 
. “Sur l’analyse micrographique des eaux,” Comptes Rendus, 14th June, 
1880, 
