and Laboratory Methods. 2719 



plates by low temperatures or allowing it to cool at the ordinary room temper- 

 ature affects the type of colony produced. In short, Dunham insists that in the 

 study of bacterial colonies it is necessary to pay the most strict attention to the 

 physical nature of the gelatin and use methods of insuring greater uniformity. 



Hastings. Milk-agar as a Medium for Dem- ^j^g ^^^y^^^ suggests the use of milk 

 onstrating the production of rroteolytic °° 



Enzymes. agar as an advantageous medium for 



detecting proteolytic enzymes. He uses skimmed milk, which is added to com- 

 mon agar, and sterilized in the ordinary way. After cooling, this makes an 

 opaque medium which may be used for slant tubes or petri dishes and upon 

 which bacteria will grow luxuriantly. When cultures of liquefying organisms 

 grow upon this medium it is rendered transparent by the digestion of the casein, 

 and bacteria which produce enzymes may thus be very readily detected. The 

 advantage of the use of this medium over the use of gelatin is chiefly that the 

 bacteria may be cultivated at high temperatures and the enzyme forming char- 

 acter therefore determined with great rapidity. The material is also adapted for 

 detecting the presence of enzymes in animal tissues, for these can be mixed with 

 the milk agar together with a small amount of antiseptic for preventing bacteria 

 growth. If enzymes are present the medium will be rendered transparent by 

 the action of the enzymes. 



Copeland. Summary of the Steps which must ^j^g ^^^^^^ i^^g S^^e useful details 

 be followed in Staining Flagella by Loemer s ° 



Method. for rendering the method of flagella 



staining more uniform. He leaves the bacteria to be tested in suspension in 



water for one or two hours to dissolve away the gelatinous capsule. He insists 



on the use of the best tannic acid, iron sulphate, and basic fuchsin for a mordant. 



These are heated to between 70 and 75°, until the steam arises to a height of two 



inches. Then the preparation fixed on a cover-glass is placed in the mordant 



for half a minute. The stain which follows must be of the best aniline oil, pure 



alcohol, and saturated alcohol solution of basic fuchsin. It must be used cold 



and the preparation must be stained in it for 8 or 10 seconds. When thus used 



Copeland is convinced that Loefiler's method of flagella staining is superior to 



any others in use. 



Winslow. Studies on Quantitative Variations Experiments with B. coli have shown 

 in Gas Production in the Fermentation Tube. ^, ., ., ., r ... 



the author the necessity of caution in 



the interpretation of the gas production in fermentation tubes. Using tubes of 



the same broth and inoculating with the same culture of B. coli Winslow found 



notable variations in the gas production. The amount of gas produced in 16 



hours varies from 20 to 62 per cent, and the amount produced in 64 hours varies 



from 38 to 80 per cent. This is not wholly due to the rapidity of gas formation, 



for the maximum production in different tubes varies from 42 to 86 per cent. 



During the first 12 hours the amount of gas produced depends upon the quantity 



of inoculated material, and the amount of hydrogen is relatively greater than at 



a later period. Between 24 and 48 hours the gas corresponds to the classical 



formula 2:4 ; after this, there is a falling off in the total amount of gas, attribut- 



