ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 589 



For making surface growths the most suitable medium is glucose- 

 pepton-agar, but any other solid medium not coagulable by heat may 

 be substituted. The vessels used are circular capsules, with an inside 

 diameter of 7 cm. and a depth of 2| cm. They are provided with a 

 flat ground flange lh cm. broad. The cover is made of plate-glass and 

 extends outwards to half the breadth of the flange, so as to leave a 

 margin uncovered. It is ground to fit closely on to the flange. In the 

 capsule is placed a layer of medium about 1 cm. thick, and then olive- 

 oil is poured in nearly up to the rim. It is then covered and sterilised. 

 When cool, the medium is inoculated by means of a pipette containing 

 pure culture. Growth is usually abundant after incubating from 24 to 

 48 hours. Such cultures may be preserved permanently by killing 

 the organisms with formalin, and then mounting the capsules with 

 refined castor-oil. 



(2) Preparing 1 Objects. 



Preserving Insects.* — In order to preserve insects collected in the 

 summer for dissection and mounting in the winter, Villagio recommends 

 the following procedure : Kill the insect in chloroform vapour, then 

 drop it into a test-tube half full of water. Raise to the boiling-point 

 and then transfer at once to 30 p.c. alcohol. After 24 hours remove 

 to a mixture of equal parts of 90 p.c. alcohol, glycerin and distilled 

 water, with \ p.c. of acetic acid added. From this fluid the insect is 

 removed to diluted alcohol for dissection, or passed through graded 

 alcohols for imbedding in paraffin. 



Preparation of Spicules of Silicious Sponges.f — R. von Lenden- 

 feld takes a piece of the sponge of the size of a hazel-nut, and boils it in 

 water. The piece of sponge is then placed in a test-tube and covered 

 with strong nitric acid. After standing for some hours it is boiled 

 until the acid is quite clear. The tube is then almost filled with dis- 

 tilled water and shaken, and after about 20 seconds the supernatant 

 fluid is decanted off into another test-tube. After some 40 seconds 

 the supernatant fluid in the second tube is removed to a third test-tube, 

 and this procedure is repeated until no spicules are obvious to the 

 naked eye. The last fluid is then centrifuged for \\ minutes. The 

 deposit is washed with distilled water several times, and afterwards 

 placed on a slide. After removing the excess of water, the preparation 

 is dried over the flame and mounted in balsam or dammar. 



Collodionage of Cells.! — CI. Regaud describes an ingenious method 

 of preparation applicable to anatomical elements naturally or artificially 

 dissociated. 



The first step consists in dissociating and fixing the cells. "When 

 dealing with a fluid rich in cells, e.g. blood, semen, etc., one or two 

 drops of the liquid are allowed to fall into several cubic centimetres 

 of a fixative, such as 1 to 2 p.c. osmic acid or 10 p.c. formalin. The 

 fixative must be kept shaken for a while to prevent agglutination of the 

 cells. If more rapidly coagulating fixatives such as chromic, picric, or 



* 



English Mechanic, Ixxix. (1904) p. 556. 

 t Zeilschr. wiss. Mikr., xxi. (1904) pp. 23-4. % Tom. cit., pp. 10-4. 



