and Laboratory Methods. '^383 



exigencies which frequently require varying heights on different stories, and as 

 generally, with the same width, the top or attic story is much reduced in height, 

 it is best to eliminate this floor, if possible, from the exhibition spaces, unless 

 top-lighted, or the architect will permit a proper spaced ceiling to be given to it. 

 It is, however, possible to produce an architectural effect, of much dignity by 

 making the top-story high-ceilinged (?), as is seen in the completed wing of the 

 Chicago Academy of Sciences (Fig. 28). 



In regard to the construction of ceilings in wide halls it is generally indis- 

 pensable to use columns, and it is the writer's opinion that while adding con- 

 spicuously to the beauty of a hall they can be so placed as not to limit its space 

 or prove an interference to cases. On the other hand, as in the large mineral 

 hall of the American Museum, huge steel girders can span the entire width of a 

 sixty foot hall, and all columns can be banished. And thirdly the construction 

 can often, in favorable positions, be domed when columns and girders are 

 equally eliminated, as is seen in the beautiful delivery hall of the PubUc Library 

 at Chicago (Fig. 29). L. P. Gratacap. 



American Museum of Natural History. ^ 



Bacteriology for High Schools. 



Copyrighted. 



IIL 



MICROSCOPICAL EXAMINATION OF BACTERIA. 



The bacteria which have developed on the potato cultures should be exam- 

 ined under the microscope so that the individuals may be seen and studied. 



There are two ways of doing this. They may be examined in a living (or un- 

 stained) condition, or they may be examined after they have been stained. 

 Each method has its distinct advantages, and both are always used in the syste- 

 matic study of any micro-organism. The latter is the least difficult and will be 

 described first. 



Preparation of Stain. The anilin dyes are used, and for ordinary puposes 

 fuchsin (magenta) methylen blue or gentian violet may be used. These dyes 

 may be purchased in a dry form, or as saturated alcoholic solutions; the latter is 

 the most convenient form. The alcoholic solution is not suited for use, but 

 must be diluted with water. This may be done by adding to nine parts of water, 

 distilled, or at least boiled, one part of the saturated alcoholic solution of the 

 stain. Or the solution may be made by placing w^ater in a test tube or vial one- 

 half inch in diameter, and then adding to this, little by little, the saturated alco- 

 holic solution of the stain until it is just opaque. 



Examination of Stained Bacteria. On a glass slide which has been well 

 cleaned, place a small drop of recently boiled water. With a platinum needle 

 or hat pin, which has been heated and allowed to cool, touch one of the colonies 

 on the potato cultures. The needle, or pin, is now introduced into the drop of 



