ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 531 



that they are usually mixed with dirt, which soon ruins the knife edge. 

 This may be got rid of by rubbing them up gently in a considerable 

 quantity of water and then decanting into a lung tube, \ to £ in. in 

 diameter, closed at the lower end with a piece of rubber tubing and a 

 burette clamp. As soon as the dirt has settled to the bottom it may be 

 drawn off. The tube may then be shaken up and the process repeated 

 until no more dirt remains. 



After being freed from dirt the alga; must be collected into a small 

 space in order that they may be imbedded. The following method * 

 has proved very successful for this purpose. A glass tube of about -] in. 

 interior diameter is first smeared at the lower end with glycerin and then 

 dipped into a solution of collodion or photoxylin. As soon as the collo- 

 dion film has become firm it is pushed down a little so as to allow the 

 end to be cut off with the scissors. An ordinary pipette bulb is now 

 attached to the upper end and the lower end is again dipped in the 

 collodion solution. As soon as it is withdrawn the bulb is compressed, 

 with the result that a collodion bubble is blown at the lower end. The 

 bulb is kept compressed until the bubble hardens into a firm sack. The 

 pipette bulb is now removed and the tube is filled with the water con- 

 taining the algse. These gradually sink down into the collodion sack, 

 which may then be compressed at the top with a pair of forceps while 

 the water is poured off. Fixing fluid may then be poured into the tube 

 and after an appropriate time got rid of in the same manner. The alga; 

 may be washed with several changes of water, in the same manner, in 

 order to remove the fixing fluid. The sack may now be held with the 

 forceps as just described and cut off close to the bottom of the tube. 

 The cut surfaces may then be brushed with a solution of collodion, 

 which serves to seal the sack. It may then be dehydrated, together with 

 the contained algse, and imbedded in the usual way. 



It often happens that the algse remain suspended in the water and 

 refuse to sink to the bottom even after some days. The addition of 

 fixing fluid to the water often causes them to sink, but even this some- 

 times fails. In such cases the author has tried the expedient of adding 

 a little white of egg, which soon coagulates, both in the water and in the 

 fixing fluid, forming a flocculent precipitate which slowly settles, carrying 

 the alga3 down with it. Very obstinate cases may be treated by partly 

 emptying the tube of water and cautiously pouring in alcohol of any 

 desired grade. This gradually diffuses downward, and when the propor- 

 tion of alcohol becomes great enough the algaj sink to the bottom. 



In many cases it is possible to concentrate the alga3 rapidly by simply 

 filtering through the Schleicher and Schiill Filter paper No. 575, either 

 with or without the use of a filter pump. This filter paper is hard and 

 smooth, and the algte, even when gelatinous, do not stick to it and can 

 be washed clown into a compact mass. Chamois skin may be used in 

 the same way ; in this case the filter pump is a necessity. The algae 

 cannot be washed clown, but can be easily removed without the slightest 

 injury (even in the case of swarm spores) by simply laying the wet 

 chamois skin flat on a board and scraping with a knife. The knife must 

 be pressed clown firmly against the chamois skin so as to squeeze out the 



* See also Strasburger's Pnicticuui, 3rd ed., p. 366. 



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