igoo-i.] The Ripening of Cheese. 115 



Barthel has recently pointed out that normal cows' milk contains 

 large numbers of leucocytes, and attributes Storch's test to their presence 

 in the milk. 



He even considered the leucocytes, or an enzyme secreted by them, 

 as the cause of the phenomena observed by Babcock and Russell and 

 by them attributed to galactase. The leucocytes also behave in the 

 same manner towards anaesthetics as galactase, and another indication 

 that the colour reaction obtained in Storch's test is due to the presence 

 of leucocytes, is that whey gives a reddish-brown and not a blue colour 

 as in the case of milk. The latter colour has been shown by Storch to 

 be due to the casein of the milk. 



Schirokich, in 1898, experimented on the diastases produced b}' 

 Tyrothrix tenuis. He grew the bacillus for four days at 35° C, and then 

 filtered the culture through a porcelain filter, and added the germ free 

 filtrate to sterilized milk. The milk was digested and the casein 

 became soluble in water, but the liquid had not the odour of cheese. 

 He then tried another method. A pure culture of a lactic acid ferment 

 was made in sterilized milk, and, as soon as complete coagulation had 

 occurred, five per cent, of the sterile diastase from Tyrothrix was added, 

 and the mixture kept at 35° C. The diastase acted slowly on the 

 casein, and at the end of fifteen days the mixture had a typical cheesy 

 smell. This experiment was repeated several times with like results. 

 Further experiments showed that the intensity of the cheesy smell 

 depended on the amount of acid present in the milk when the diastase 

 was added. 



In conclusion, Schirokich suggested the use of pure cultures of lactic 

 acid together with digesting bacteria and casein, as the ripening seemed 

 to be a special kind of .symbiosis. 



In a series of articles in the Milch Zeitung (1899) Weigmann 

 discussed the role of the lactic acid bacteria in the ripening of cheese, 

 esfjecially referring to the work of de Freudenreich. He drew the 

 following conclusions, from his own experiments and also those of 

 other investigators : 



1. The special lactic acid bacteria are not cheese ripening bacteria, 

 the form used by de Freudenreich in his experiments being only 

 facultative, or more probably degenerate lactic acid bacteria. 



2. Lactic acid bacteria have an important role in cheese ripening, 

 not in actually taking part in the ripening, but by directing the process 

 in the right direction. 



