igoo-i.] The Ripening of Cheese. 129 



this germ to belong to the aerogenes group, but the forms of this 

 bacterium that I have met with in Canadian cheese show considerable 

 variations from the type, especially with regard to the appearance of the 

 gelatine colonies which simulate rather that of B. acidi lactici (Esten). 



This group does not increase in cheese and I have not found them 

 in cheese older than thirty days. 



TJie liquefyinf^ bacteria found in Canadian cheese were not numerous, 

 and their numbers decreased as the cheese ripened, so that in three 

 weeks old cheese they were seldom found. A constant endeavour was 

 made in order to isolate micro-organisms belonging to this class, but 

 usually without success. On one occasion the presence of a larger 

 number of digesting bacteria than usual was associated with a bad 

 flavour in the cheese. 



Some seven different species of liquefying germs have been isolated. 

 Probably the commonest species were forms almost identical with 

 Hueppe's Bacillus btityricus. This germ was several times found in fair 

 numbers, from cheese taken from very warm curing rooms. The next 

 most common species was a Clostridium form, which grew in long 

 threads. On gelatine, it formed a brown granular colony, and milk was 

 completely digested. It might belong to Duclaux's Tyrothrix group. 



What was evidently a variety of Conn's B. varians lactis was also 

 isolated. 



Two or three forms met with seemed allied to the Proteus group, 

 and seemed to be closely related to B. fulvus (Zimmermann). These 

 were found only in young cheese. 



Practically the whole of this group gave rise to bad flavour or odours 

 in milk. Butter has been made from cream ripened with some of these 

 bacteria, and invariably a bad product was produced 



Yeasts. 



I have found yeasts quite commonly present in Canadian cheese, 

 and frequently in large numbers. This fact was first noted whilst 

 studying at Wisconsin University in Professor Russell's laboratory, but 

 no special endeavour was then made to give them the best conditions 

 for growth. Since, I have used yeast water gelatine, and ale wort 

 gelatine, for their isolation. The latter medium is excellent, as other 

 bacteria that may be present in the sample do not find it a suitable 

 pabulum. 

 9 



