568 



CONTRIBUTION TO OUR KNOWLEDGE OF THE 

 ACTION OF RENNIN. 



By A. H. Moselby, M.B., Junior Demonstrator of Physiology 

 in the University of Sydney, and H. G. Chapman, M.D., 

 B.S., Demonstrator of Physiology in the University of 

 Sydney. 



(From the Physiological Laboratory of the University of Sydney). 



In the course of some experiments upon the clotting of milk, 

 it was noted, that when milk which was bought in Sydney and 

 which showed an acid reaction to litmus was neutralised with 

 alkali, rennin ceased to produce its customary clot. Further, it 

 was found that the addition- of quantities of alkali insufficient to 

 produce neutrality of reaction to litmus inhibited the clotting of 

 the milk with rennin. This investigation was undertaken to 

 ascertain the cause of this phenomenon and to study the circum- 

 stances which modified its occurrence. 



Methods. — For all experiments a sample of rennet which pos- 

 sessed considerable potency and which had been in the laboratory 

 for some years was utilised. The milk which was bought in 

 Sydney varied in acidity with different samples. The acidity 

 was determined after the addition of 1 c.c. phenol-phthalein to 

 25 c.c. milk by titration with —NaOH until a pink colour 

 appeared.* All measurements were made from burettes, so that 

 strict quantitative conditions were observed. Water-baths were 

 arranged to keep a constant temperature of 40°C. The test- 

 tubes were examined frequently at definite intervals of time to 

 determine clotting. That time at which the test-tube could be 



* Winter Blyth, "Foods, their Composition and Analysis." London, 1903, 

 p. 230. 



