Septembee 3, 1915] 



SCIENCE 



321 



The flasks were sterilized under 15 pounds of 

 steam pressure for 15 minutes. After this steriliza- 

 tion, the compounds were introduced into the flasks 

 in desired concentrations and all flasks received 

 equal inoculation of pure cultures of Azotoiaoter 

 previously grown on Ashby's agar and suspended 

 in sterile water. Two flasks were set up for each 

 compound in every concentration and two control 

 flasks receiving only inoculation were used to test 

 the fixation power of the culture used. All flasks 

 were incubated for 21 days, at the end of which 

 time nitrogen determinations of the content of 

 each flask were made by the Kjeldahl method. 



In studying compounds which contain nitrogen 

 four flasks instead of two were set up with each 

 compound, two of the flasks receiving inoculation 

 with Azotobacter and the remaining two used as 

 controls for the nitrogen content of the compound — 

 these latter flasks were kept in the incubator room 

 during the period of incubation. 



The concentrations employed were on the basis 

 of p.p. Mil. or 0.025, 0.05, 0.1 and 0.2 gram per 

 liter. 



The results of the study indicate that fixation 

 of nitrogen by Azotobacter is only slightly in- 

 fluenced by most of the compounds investigated. 



Hydroquinone and salicylic aldehyde revealed 

 the most toxic properties of any compounds stud- 

 ied. 



Esculin, quinie acid and bomeol afforded 

 marked stimulation to the growth of the organ- 

 ism. 



The efEeets of the compounds on Azotobacter 

 are not, as a rule, in ai.;ord with what has been 

 reported of their action on the higher plants. In 

 concentrations which are fatal to certain higher 

 plants, many of the compounds only slightly de- 

 pressed fixation. 



Such compounds as nicotine, picoline, guanidine 

 and skatol exhibited toxic properties commensurate 

 to those usually ascribed to these substances. 

 Caffeine appeared to stimulate the growth of the 

 organism. 



Many of the nitrogenous compounds used which 

 Lave been reported as beneficial to higher plants 

 exercised a marked depression on fixation. It ap- 

 pears that the simpler compounds were more 

 pronounced in this respect than were the more 

 complex ones. It is suggested that this condition 

 is not one of toxicity, but that the nitrogen of the 

 compounds was utilized by Azotobacter in pref- 

 erence to that of the atmosphere. Urea, glycocoll, 

 formamide and allantoin were especially active 

 ia -depressing fixation. 



Belation of Numbers of Streptococcus lacticus to 



Amount of Acid Formed in Milk and Cream: 



P. G. Heinemann. 



Erlenmeyer flasks were filled with 250 o.c. each 

 of milk and cream. Three flasks of each series 

 were sterilized and then inoculated with a culture 

 of Str. lacticus in litmus milk. Three flasks of raw 

 milk and cream were also inoculated. Three flasks 

 of each were left to sour spontaneously. The 

 flasks were incubated at three different tempera- 

 tures, 37°, 20° and 7°. Plates were prepared 

 from the original milk or cream and the number 

 of bacteria counted. The acidity was determined 

 by titration with one twentieth normal sodium 

 hydrate phenolphthalein as indicator. Every day 

 for ten days the milk was titrated and counts 

 made by plating. The determinations were made 

 with the cream for eight days. 



The following facts were observed: 



1. The amount of acid formed during the sour- 

 ing process of milk or cream is not solely de- 

 pendent upon the number of bacteria present of 

 the Str. lacticus group. Temperature and the 

 presence of other bacteria may influence the re- 

 sult. 



2. In raw milk or cream or in raw milk or 

 cream inoculated with cultures of Str. lacticus 

 the number of bacteria increases to a given point 

 and then decreases. The higher the temperature 

 up to 37° C. the earlier is the maximum num- 

 ber reached. 



3. Coagulation of milk or cream is not depend- 

 ent solely upon a certain amount of acid or a 

 certain number of bacteria. 



4. After the decline in numbers the amount of 

 acid continues to increase, probably due to 

 enzyme action. 



5. At 37° extraordinarily large amounts of acid 

 may be formed, due probably to the presence of 

 members of the group of lacto -bacilli. 



The Variability of Two Strains of Streptococcus 



Lacticus: P. G. Heinemann. 



The present investigation was conducted to deter- 

 mine the possibility of varying the fermentative 

 power of Str. lacticus by animal passage. Two 

 strains were isolated and inoculated into rab- 

 bits and guinea-pigs. The amount of acid pro- 

 duced by the original culture was determined by 

 titration after three days' incubation at 37° C. 

 After each passage the recovered organism was 

 again inoculated into the solutions of test sub- 

 stances and the acid determined again. The 

 amount of available free oxygen was regulated by 

 filling nessler tubes with definite amounts of the 



