622 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. [16] 



Osmic acid as a Mlling and hardening agent for infusorians and small em- 

 bryos. — The use of osmic acid in the stady of the development of AmpM- 

 axus, by Hatschek, has given very good results. During their early stages 

 the embryos of this creature are quite small, and swim about in the sea 

 water in which they have been hatched, Hatschek killed the embryos and 

 hardened them in the following manner : A few drops of a 1 per cent, 

 solution of osmic acid was poured into the small vessel of sea water 

 containing the embryos, and allowed to act only a short time. This 

 killed the embryos and hardened them, and also affoixled a ready means 

 of collecting them, for as soon as they were dead they fell to the bot- 

 tom of the vessel and were then easily picked up with a pipette, or the 

 supernatant mixture of sea water and osmic acid was poured off and 

 replaced with fresh sea water two or three times, so as to wash off the 

 acid and arrest its further action. They were then transferred to abso- 

 lute alcohol and finally to oil of cloves. 



The embryos were embedded in wax and oil on a slide thinly coated 

 with clove oil. A single drop of a mixture of wax and oil (beeswax 

 and oil equal parts) is dropped on the embryo, when its position may 

 he arranged on the slide by turning the congealed drop of wax. He cov- 

 ered the whole slide, which was greasy with oil, with a coating of the 

 melted wax and oil. The position of the embryo is then carefully 

 marked with needle scratches. The mass is then slipped off of the 

 slide and covered on the opposite side with another coat of wax and 

 oil. To prevent the two halves of wax from separating, it is a good 

 practice to pass a hot needle through both at different points in order 

 to bind them together. The sections are then cut by hand, which,' 

 judging from Hatschek's figures, was very successfully done. 



M. Adrien Certes has used osmic acid in order to kill and precipitate 

 infusorians and other minute organisms found in fresh and salt water 

 with gratifying results. One cubic centimeter of a 1 per cent, solution 

 of osmic acid he finds sufficient to kill the minute animal and vegetable 

 organisms in 30 to 40 cubic centimeters of water, these organisms be- 

 ing precipitated to the bottom of the vessel and fixed in their form. The 

 acid must not be allowed to act too long, and to prevent this an equal 

 volume of distilled water is added to the mixture after the organisms 

 have been killed. 



In the case of some waters rich in organisms, microsopic examination of 

 the deposit so obtained may begin after a few hours. In the case of 

 very pure water it may be necessary to wait for twenty-four or even 

 forty-eight hours before the supernatant liquid may be poured yff' and 

 the precipitated organisms examined. 



It affords a very ready way of killing and coll cting very minute or- 

 ganisms from either fresh or sea water. This .aethod may also be used 

 to precipitate bacteria or other supposed hurtful organisms from sus- 

 pected potable waters. 



