126 THE AMERICAN MONTHLY [June, 



series of cultivations. The jelly is allowed to solidify in tubes placed 

 perpendicularly. 



For separating bacteria from one another in a mixture, or for study- 

 ing the peculiarities of certain forms, plate cultivations are preferable. 



For glass slide cultivations the ordinary microscopic slides may be 

 employed. After sterilization in the usual manner, they are kept, after 

 inoculation, on glass trays in glass vessels. When using the jelly in 

 these cultivations, it is first liquified and then poured out on the glass 

 slides. When it has solidified, a platinum wire, bent at the end, and 

 dipped in the material to be tested, is lightly and rapidly drawn over 

 the surface. As the wire passes over the surface of the jelly it leaves 

 the bacteria along its track. 



Blood serum as a cultivating medium is mainly limited to tubercle 

 and glanders bacilli. 



Pastes are very useful, especially for fungi. They may be made of 

 crushed potato, bread, various fruits, etc. 



Cultivations of the various micro-organisms may be obtained pure 

 from mixtures of various kinds — such as are commonly found in decom- 

 posing materials, etc. It is best, however, to get pathogenic organisms 

 from the body of the animal affected. 



In examining earth for bacteria, it should not be forgotten that they 

 are close to the surface, and that only spores and anaerobes are deep 

 down. 



In testing water both the numbers and the kinds of bacteria present 

 must be taken into consideration. The vessels in which the water to 

 be tested is received must, of course, be sterilized before the water is 

 introduced. 



For testing air, Hueppe's method is one of the best. " He aspirates 

 a definite quantity of air through a certain amount of culture fluid, and 

 then, shaking the flask well to distribute the bacteria equally through 

 the fluid, he makes plate cultivations with known quantities of the 

 fluid in nutrient jelly and agar, testing the mixture of air and culture 

 fluid in the same way that water is tested." 



Detecting Alterations in Manuscripts. — As accessory to the use 

 of the microscope, the use of photography is recommended by Mr. 

 Geo. G. Rockwood, of 17 Union Square, New York. He has for 

 years been in the habit of photographing manuscripts, models, books 

 of account, checks, and drafts, whenever their genuineness was ques- 

 tioned. The process sometimes makes legible figures, amendments, 

 and alterations which even the microscope does not fully bring out. 

 This is due to the extreme sensitiveness of photographic plates to 

 shades of color. With the new " Autho-chromatic" or color-sensitive 

 plates almost imperceptible stains on old yellow paper have been made 

 clear and legible. 



(Our Utah friend, whose signature to a will was tampered with, may 

 like to consult Mr. Rockwood.) 



