March 6, 1903.] 



SCIENCE. 



373 



inasmuch as it can be incubated at high 

 temperatures. 



If cultures of a liquefying organism be 

 made in this medium, the growth after a 

 few houi's' incubation wiU be surroiuided 

 by a transparent zone due to the liquefac- 

 tion of the casein. 



Its advantages over gelatin are that it 

 can be incubated at any temperature; that 

 the liquefying power of organisms whose 

 optimum temperature zone lies above 20° 

 C. can be determined in a much shorter 

 time than by the use of gelatin. 



It can also be used to determine the 

 presence of proteolytic enzjaues in plant 

 and animal tissues by adding cubes of milk- 

 agar to the extracts of such tissues, in the 

 presence of suitable antiseptics, such as 

 small amounts of carbolic acid or formalin. 

 The presence of proteolytic enzymes is 

 made apparent by the edges of the cubes 

 becoming transparent. 



Laboratory Notes: W. M. Esten, Middle- 

 town, Conn. 



A new thermo-regulator for incubators 

 heated with incandescent lamps was con- 

 structed from a description by Mr. H. E. 

 Ward, of the Illinois Experiment Station. 

 This was shown and its regulating quality 

 demonstrated. Its advantages are that the 

 heat is applied to the interior, and that in- 

 cubators can be constructed of wood and 

 danger from fire avoided. 



New Method of Preparing Blue-Utmus- 

 lactose-gelatin.—H'he cooking and steriliz- 

 ing of litmus with gelatin proves to be 

 detrimental to the reaction of litmus. The 

 litmus and gelatin media are prepared and 

 sterilized separately, then mixed immedi- 

 ately before plating. Fifteen to twenty 

 per cent, of litmus is digested in distilled 

 water for several hours at 70° C, filtered, 

 the reaction adjusted to + 1-5 per cent., 

 and sterilized. A gelatin medium is pre- 

 pared with 3 per cent, lactose and 25 per 



cent, less water than ordinary gelatin. 

 Tubes are filled with 8 c.c. of gelatin. 



Cheese-whey-gelatin is prepared by add- 

 ing rennet to fresh skim milk. The whey 

 is placed in an autoclave for thirty minutes 

 at 105° C. Ten or eleven per cent, of 

 gelatin is added and the medium cooked in 

 open dish until one-fourth is evaporated; 

 the reaction is adjusted to + 1.5 per cent., 

 and tubes filled with 8 c.c. 



To prepare the gelatin tubes for plate 

 ciiltures, place in each tube of melted gela- 

 tin with sterile pipette 2 c.c. of the litmus 

 solution, mix and add 1 c.c. of diluted 

 milk, and plate. 



The comparative values of the two kinds 

 of gelatin are that the lactose-litmus-gela- 

 tin gives the maximum numbers while the 

 cheese-whey-litmus-gelatin gives a strong 

 differentiation of acid and non-acid species. 

 To get the advantages of both kinds of 

 gelatin mixing half and half proves very 

 satisfactory'. 



It is possible by means of this mixed 

 gelatin to classify the different kinds of 

 bacteria on the plates by means of the 

 colonies alone. 



The 'Germicidal Property' of Milk: W. A. 



Stocking, Jr., Middletown, Conn. 



Freudenreich, Park, Hunziker and others 

 have sho'wn that cows' milk, when a few 

 hours old, contains a smaller niunber of 

 bacteria than when freshly drawn from the 

 coAV. From this they conclude that milk 

 possesses a 'germicidal property or action' 

 during the first few hours. This conclu- 

 sion was based on the results obtained from 

 agar plate ci;ltures, on which the total num- 

 bers of bacteria were determined. These 

 investigators, however, were unable to ex- 

 plain the cause of this phenomenon. The 

 purpose of the experiments described in 

 this paper was to determine, if possible, 

 the cause of this dropping out of the organ- 



