336 The Microscope. 



by a little ring of clear space, distinctly visible ; the slip will be 

 irregularly and minutely speckled. Have the surface unspotted 

 and it will be clean as possible. 



The dealer's slips are not very dirty, but they must be made 

 less so. The books recommend many preparations, compounded 

 of many and various chemicals, to be used for this purpose. 

 But the slips are seldom dirty enough to need any special treat- 

 ment. A bath of warm water and soap, with a thorough wash- 

 ing afterward, is about all they will require. If spots should re- 

 sist this treatment, then the microscopist has always by him an 

 ever-ready fluid that he can use with success. For cleaning 

 glass there is scarcely anj^thing better than this fluid. It will 

 often remove stains and spots that will resist acids. It is his 

 own saliva. Of course it must be as Nature intended it to be, 

 and as the healthy glands secrete it. 



In the books will be found many chemical mixtures recom- 

 mended for this purpose, yet few of them are used, except by 

 their devisers. Dr. F. L. James, a microscopist of experience, 

 recommends the following as a good cleaning fluid for refrac- 

 tory slips. He finds it particularly valuable if they are to be 

 used for making mounts with glycerine, since that is a rather 

 troublesome medium to work with, as the reader will leai'u here- 

 after. The following is Dr. James' receipt. He takes a wide- 

 mouthed jar and half fills it with a mixture of gasoline, (or ben- 

 zine,) turpentine and benzol. The slips are left in this all night. 

 When convenient, take out each slide separately, give it a good 

 hard wipe with a piece of muslin, and polish it with another 

 piece. " Try this plan once," says Dr. James, " and you will 

 never use any other. Slides thoroughly cleaned thus, possess a 

 quality which, in making aqueous or glycerine mounts, is abso- 

 lutely invaluable. White they ai'e opticall}^ and practically 

 clean, such slides retain upon their surface an exceedingly tenuous 

 film of resinous matter that prevents water or gl3-cerine from 

 attaching itself to the surface, and the consequence is that the 

 surplus fluid, after a cell is ijlosed, rolls off" the slide without 

 moistening it in the least. Cement, on the contrarj^, attaches 

 itself with extraordinary firmness and evenness." A strong 

 solution in water, of common washing soda, has also been recom- 

 mended for this purpose. The slips are placed in it and left 

 there for an indefinite time. Care should be taken that the solu- 



