98 PKACTICAL PHYSIOLOGY. [XIII. 



To B a few drops of lo per cent, solution of calcium chloride — no clot of 

 casein. 



To C rennet and calcium chloride — clot of casein, 



10. Opacity of Milk — Vogel's Lactoscope. 



Apparatus required. — A graduated cylindrical cc. measure to hold 200 cc. ; 

 a lactoscope, with parallel glass sides, 5 mm. apart (fig. 50) ; a burette finely 

 graduated : a stearin candle. 



Method. — (a.) Be certain, by microscopical examination, that the milk 

 contains no starch, or chalk, or other granular impurity. 

 {b.) Mix 3 cc. of milk with 100 cc. of water in the 

 cylindrical measuring glass. 



(c.) In a dark room place the lactoscope on a table, 

 and I metre distant from it a lighted stearin candle. 

 Fill the lactoscope with the diluted milk, and look at 

 the candle flame through the glass. If the contour of 

 -Lactoscope. the flame can be seen distinctly, pour back the diluted 

 milk into the bottle, and add another cc. of milk. Mix 

 again. Test the mixture again, and repeat until, on looking through the 

 glass, the outline of the candle-flame can no longer be recognised. Add 

 together the quantities of milk used. An empirical table constructed by 

 Vogel gives the percentage of fat. 



11. Wheaten Flour. — According to Martin, gluten as such does 

 not exist in flour. It appears that the two proteids which it con- 

 tains — vegetable myosin and an albumose — when mixed with water 

 undergo certain changes, and become converted into the insoluble 

 proteid gluten. 



(a.) Gluten. — Moisten some flour with water until it forms a 

 bough tenacious dough ; tie it in a piece of muslin, and knead it in 

 a vessel containing water until all the starch is separated. There 

 remains on the muslin a greyish- white, sticky, elastic mass of 

 "crude gluten," consisting of the insoluble albumenoids, some of 

 the ash, and the fats. Draw out some of the gluten into threads, 

 and observe its tenacious characters. 



(b.) Dry some of the gluten, and heat it strongly in a test-tube ; 

 an ammoniacal odour similar to that of burned feathers is evolved. 

 Water, which is alkaline (due to ammonia), condenses in the upper 

 part of the tube. 



(c.) Extract 10 grams of wheaten flour with 50 cc. of water in 

 a large flask. Shake it from time to time, and allow it to stand 

 for several hours. Filter. If the filtrate is not quite clear, filter 

 again. Heat a part of the clear filtrate, and observe the coagula- 

 tion of vegetable albumin. 



(d.) Test another portion of the filtrate from (c.) for the xantho- 

 proteic reaction. 



(e.) Another portion of (c.) is to be precipitated by acetic acid 

 and ferro-cyanide of potassium. 



(/.) Test a third portion of (c.) for the reaction with NaHO and 



