ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 499 



but this joint should be easily separable. In operation we take up a 

 small portion of the material in a dropper, and squeezing it into the 

 vial, we insert the rubber tip of the glass tube, and holding the strainer 

 under water, press on the bulb, which will cause the air, acid, and salts 

 to flow out together with a cloud of fine waste material. The pressure 

 is now to be alternately applied and released, and the waste material is 

 thus gradually removed. The discharge of clay and fine sand at last 

 ceases, and the diatoms are left with the coarse sand and mica which 

 can be removed by other means. 



By thus eliminating the clay we will have disposed of one of the 

 most serious obstacles to the cleaning of diatoms. One very important 

 advantage of this method of working is the small quantity of material 

 required, because there is vory little waste. Successive portions as they 

 are cleared can be united to nuike up the needed amount. 



It is important that the strainer should not be overloaded, for that 

 would cause it to pack and choke. This pack has to be broken up by 

 shaking after each compression, more particularly in cleaning filamentous 

 forms, in order to allow the imprisoned debris to escape at the next 

 compression. As a general rule, and with the more granular forms, 

 this packing requires only a little attention to avoid trouble. Violent 

 compression will fracture many of the larger and more fragile forms of 

 diatoms. The strainer vial should be kept in water when not in use, to 

 avoid injury to the wood-section from contraction. 



After the section has been in use for a considerable time the pores 

 gradually become stopped with fine sand. Clay alone does not cause 

 this condition. The only remedy is to cement on a new section. 



An interesting point in this connexion is that when we burn an old 

 strainer-section for the purpose of studying this clogged condition, we 

 find that the ash will crumble if dampened, and will fall into numerous 

 " sticks," each the length and diameter of a pore of the wood, and each 

 of these " sticks " will be found to be packed with the small sand grains. 



It may be said in regard to the selection of wood, that white pine — 

 Pinus strobus — is excellent for ordinary use, since the strainers cut 

 therefrom work freely. Certain light diatoms that would as a rule have 

 been floated away in the usual settling and pouring-off process, are 

 here retained by the pine section, because their length enables them to 

 bridge across the pores. Some very short forms, however, will pass 

 through to a considerable extent. 



By saving the tailings from the pine and passing them through a 

 spruce strainer, the majority of these short forms were retained. The 

 spruce here referred to was a piece of flooring, and of a very white 

 species of spruce. It was not identified. There are several other species 

 that would probably answer equally well. In using spruce, the sections 

 should be thin. The clay will be found to pass through the pores of 

 spruce with some freedom, but not so rapidly as through pine. 



There are some gatherings that will require a strainer of still finer 

 grain. This may be said of the very smallest diatoms that grow on 

 water plants. The majority of these may be retained by a quite thin 

 section cut from the white outer wood of the red cedar Juniperus 

 Virginiana. In one experiment some of these very minute forms 



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