54 



CHEMICAL PHYSIOLOGY. 



the mass, 

 fluid. 



Within a few minutes the whole becomes 



(c.) After a short time fifteen to twenty minutes before 

 the peptonisation is complete, filter and exactly neutralise the 

 filtrate with ammonia, which precipitates the antialbumpse 

 and hemialbumose. Dissolve these in a 5 per cent, solution 

 of sodic chloride. To isolate the hemialbumose, precipitate 



it with nitric acid, or dialyse 

 the salt solution of it in a parch- 

 ment-paper tube arranged in 

 Kuhne's dialyser (Fig. 10). The 

 greater part of the hemialbumose 

 is thrown down in flocculi on 

 the parchment tube. 



(d.) The filtrate after neutral- 

 isation is evaporated, and yields 

 peptones, which can be precipi- 

 tated by alcohol. 



6. Action of Gastric Juice on Milk. 



(a.) Place 5 cc. of fresh milk 

 in a test-tube, and add to it a 

 few drops of a neutral artificial 

 gastric juice. Mix and keep at 

 40 C. In a short time the milk 

 curdles, so that the tube can be 

 inverted without the curd fall- 

 Fig- 10. i n g out. By-and-by whey is 

 Kiihne's Dialyser. squeezed out of the clot. The 

 curdling of milk by the rennet 



ferment present in the gastric juice is quite different from 

 that produced by the "souring of milk," or by the precipi- 

 tation of casein by acids. Here the casein (carrying with it 

 most of the fats) is precipitated in a neutral fluid. 



(b.) To the test-tube add 5 cc. of 0-4 per cent, hydrochloric 

 acid, and keep at 40 C. for two hours. The pepsin in the 

 presence of the acid digests the casein, gradually dissolving 

 it, forming a straw-yellow coloured fluid containing peptones. 

 The " peptonised milk " has a peculiar odour and bitter 

 taste. 



