746 SUMMARY OF CURRENT RESEARCHES RELATING TO 



to expose the organisms on the slide for five 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. 



Certes * 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 droj>s 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. In a 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 alg?e, spores, bacteria, monads, vibriones, 

 amoebfe, 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 Monas 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 Kay Lankester, are contractile, and whether 

 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- 

 glasses a drop of osmic acid properly diluted, and then added to it 

 distilled water. 



When, after a rest of twenty-four hours, we coloured the organisms 

 in the latter glass by means of reagents, of which we shall speak later, 

 we succeeded in showing the long filaments. This was, on the con- 

 trary, impossible with the organisms in the other glass ; a phenomenon 

 which we attribute to a contraction of the filament in the latter case, 

 and to an absence of contraction in the case of fixation by osmic 



acid.t 



Alcoholic solution of corrosive sublimate. — The effect of this solution 

 employed as a fixative is rapid, but of very short duration. It is 

 used with advantage in studying aleurone. 



III. CONTEACTION. 



It is known that protoplasm, either free like the plasmodia of the 

 Myxomycetes, or surrounded by a ternary membrane, as in multi- 

 cellular plants, has at its periphery a hyaline layer, which remains 

 in perfect continuity with the rest of the protoplasm, though dis- 



* " Sur I'analyse micrographique des eaux," Comptes Keiidus, 14th June, 1880. 

 t Bull. Soc. Bot., iii., 22nd July, 1881. See this Journal, ii. (1882) p. 640. 



