54 TEXT-BOOK OF BACTERIOLOGY. 



blue, in powder, is added. Two or three drops of this solution must 

 be filtered upon the cover-glass. 



To act satisfactorily the color must be applied hot; it is then 

 rinsed with water and the preparation at once examined. 



Not only the cover-glasses, but also the tissues in which bacteria 

 are to be sought require special preparation for the staining proc- 

 ess. They cannot be used just as they come from an animal im- 

 mediately after death. For the determination of the simple ques- 

 tion as to whether bacteria are present or not, the easily-made 

 "smears" are far better. The bacteriologist, therefore, has no oc- 

 casion to use fresh tissues for instance, sections made with a freez- 

 ing microtome which indeed, as a rule, do not even show the micro- 

 organisms themselves, much less the details of their structure. 



Portions of the organs about as large as nuts, while still as fresh 

 as possible and before putrefaction and decomposition have begun, 

 are placed in absolute alcohol to harden them. 



The alcohol must be perfectly anhydrous. It is therefore desir- 

 able to lay some blotting-paper in the vessels for the reception of 

 portions removed from the various organs, and to laj- su,ch portions 

 on the blotting-paper; for if the alcohol imbibes water out of the air 

 and out of the portions thrown into it, the diluted part of the alcohol, 

 being heavier, sinks to the bottom under the blotting-paper, while 

 the portions to be hardened remain above in the anhydrous strata. 



When they have remained about two days in the alcohol, which 

 has been changed once or several times, according to circumstances, 

 they are properly hardened; the'aicohol has caused their fluid albu- 

 min, glutin, miicin, etc., to coagulate, and has withdrawn the w r ater 

 from their tissues. 



The hardened portions are now fastened to small corks with 

 some adhesive substance. A mixture of glycerin and gelatin has 

 been found very suitable for this purpose : one part gelatin, two 

 parts water, and four of gtycerin are dissolved Toy heat and boiled 

 to a thick consistency, after which the mixture is ready for use. A 

 drop of it is placed upon the cork, the hardened portion pressed 

 down upon the drop and allowed to cool for a few moments, and 

 then the whole is once more placed in the alcohol. 



After two or three hours the preparation is ready for further 

 manipulation. 



To examine such an object, first cut it up into a number of the 

 thinnest possible sections. For this purpose employ one or other 

 of the many kinds of microtomes now manufactured.* He who 



* Bausch and Lomb, of Rochester, N. Y., manufacture several styles of 

 these instruments, which are quite reliable. J. H. L. 



