70 Bacterial Bl'ujht of Pear B1o>isoins in South Africa 



Cohn^s solution. No growth. 



Potato. A creamy-white, wet-shining streak about 6 — 8 mm. 

 broad appears along the needle track ; the edges are undulate. 



Turnip. On turnip there is a thin, wet-looking, whitish growth, 

 almost covering the slant surface. 



Beet. On beet the growth is heavier than on turnip and carrot 

 but it is not so spreading ; it is yellowish and slightly raised. 



Carrot. There is a very thin, whitish, wet-looking growth, in some 

 tubes almost completely covering the slant surface ; in others where 

 the cylinder was drier only producing a streak a "few millimetres wide 

 along the needle track. 



Parsnip. On parsnip there is a good growth along the needle 

 track, 5 — 10 mm. wide, and slightly raised, shining. 



Physical and Biochemical Relations. 



Proteolytic activity. It has been pointed out in the section dealing 

 with the cultural characters of the organism that milk is slowly pep- 

 tonised. If a ten days old culture of the organism is killed by exposing 

 it to a temperature of about 55° C. for half an hour and then 3 — 5 c.c. 

 of the culture run into each of a number of tubes of sterile litmus milk, 

 it is found that the milk is slowly cleared in precisely the same way as 

 if the organism were growing in the medium. 



A series of flask cultivations was carried out with a view to testing 

 for the products of proteolysis. The media used were ordinary nutrient 

 broth, egg albumen (1 gm. in 50 c.c. of -05 % potassium phosphate) 

 and milk ; in each case 50 c.c. of the medium being sterilised in an 

 Erlenmeyer flask of about 150 c.c. capacity. In this way the organism 

 received abundant aeration and growth was fairly rapid. 



Cultures in nutrient broth were tested for ammonia by distillation 

 after five days at 25° C. The Nessler test could not be used owing to 

 the presence of an appreciable amount of ammonia in the control 

 flask. 



A quantitative test showed that the amount of ammonia in the 

 culture had not increased from the fifth to the tenth day, the difference 

 in each case between the amount of ammonia in the culture flask and 

 the control being -016 grm. of ammonia nitrogen. 



Egg albumen after five days at 25° C. gave a definite reaction for 

 peptone and for tryptophane. The culture was tested by Sorensen's 

 method for amino-acids and ammonia together at the end of the fifth 

 and the tenth day. After five days the result was -0148 grm. nitrogen 



