634 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



for some time ; on standing, the ethereal solution of the liberated fat rises to the 

 surface and is to be carefully decanted into a weighed porcelain dish. Some more 

 ether is to be added to the alkaline milk, and after vigorous agitation it also is to 

 be transferred, as before, to the capsule. The same process may be repeated 

 several times if necessary. The ethereal extract is now evaporated over a water- 

 bath, and after having been dried in an air-bath at 110° the weight of the residue 

 is to be ascertained ; this multiplied by 5 gives the percentage. With cows' milk 

 it varies between 2 and 5 per cent., but the normal minimum for fats is about 2.75 

 (Cameron). 



3. Tlie Casein and Albumen. — (j.) (a) Dilute twenty cubic centimeters milk 

 with four hundred cubic centimeters water, and treat the mixture with very dilute 

 acetic acid, added drop by drop, until a flocculent precipitate begins to appear. 

 Now pass a current of carbonic acid gas through the fluid for fifteen to thirty 

 minutes and lay aside for one or two days. Collect the precipitated casein on a 

 weighed filter, wash it with spirit, and then with ether until a drop of the wash- 

 ings leaves no fatty stain on paper ; dry at 100° and weigh. Subtract the weight 

 of the filter, and the difference multiplied by 5 gives the percentage of casein. In 

 human milk, precipitate the casein by saturating with magnesic sulphate. 



(6) The nitrate from the casein precipitate is to be concentrated to a small 

 bulk over a water-bath and an acetic acid tannin solution added so long as any 

 precipitate occurs ; after the precipitate has settled, collect it on a weighed filter, 

 where it is to be washed with dilute spirit until the filtrate gives no blue coloration 

 with ferric chloride (indicating absence of tannin) ; dry now at 100° and weigh. 

 The weight multiplied by 5 gives the percentage of albumen. 



In cows' milk the casein varies between 3.3 and 6 per cent., and the other 

 albumens from 0.3 to 0.4 per cent. In diseased milk the casein may be as low as 

 0.2 per cent., and the other albumens as high as 10 per cent. 



(ij.) (a) Ten cubic centimeters milk are diluted with one hundred cubic cen- 

 timeters distilled water and well mixed ; a copper solution, made by dissolving 

 sixty-three and five-tenths grammes of cupric sulphate in one liter of water, is 

 then added slowly with stirring until the coagulum begins to settle quickly. The 

 whole mixture, together with half the cupric sulphate solution already employed, 

 is then added to some potash solution (fifty grammes of potash to the liter), and 

 after a short interval the clear fluid is filtered off through a filter dried at 110° C. ; 

 the precipitate is washed until the washings amount to two hundred and fifty 

 cubic centimeters, and the sugar is to be estimated in this subsequently. 



(b) The coagulum on the filter is next treated with absolute alcohol, slowly 

 dried, and extracted with ether ; the ethereal and alcoholic extracts are then to be 

 distilled, and the fatty residue dried and weighed. The coagulum, after having 

 been dried at 125°, is weighed, then ignited, the ash deducted, and the difference 

 taken as pure albuminoid (Ritthausen). 



4. The Sugar. — (j) Take twenty-five grammes of milk, acidify with hydro- 

 chloric acid, boil, and filter, washing the coagulum with water; to convert the 

 milk-sugar into glucose, boil the filtrate and washings for an hour or so in a flask, 

 to the mouth of which a long tube has been attached. When the liquid cools, 

 make its volume up to two hundred cubic centimeters and determine the sugar 

 by Fehling's method, measuring twenty cubic centimeters Fehling's solution into 

 a flask, diluting with eighty cubic centimeters water, and to the boiling mixture 

 add the diluted filtrate from a Mohr's burette until the copper is entirely reduced. 



(ij.) This sugar determination may be readily effected by the polariscope. 

 Measure forty cubic centimeters milk into a flask of one hundred cubic centimeters 

 capacity, add some carbonate of sodium if the milk is not alkaline, and then 

 twenty cubic centimeters moderately concentrated solution of neutral acetate of 

 lead, and shake well ; having next fitted the neck of the flask to a long glass tube 

 or to the condenser of a Liebig's still, boil it over a small flame ; then filter, and 

 test the filtrate with the polariscope. With a one-decimeter tube the percentage 

 of sugar is obtained by multiplying the rotation by 1.44. 



* For other ready methods of milk analysis and for the detection of foreign substances 

 with which milk may be adulterated the reader is referred to the following articles :— C. Storch, 

 Oesterreieher Vierteljahresschri.fi fur Wissen ; Teterinarkunde, 1884, Hef te II., s. 195 ; Arch, 

 f. Tliierheilkunde, 1885, Hef te 5 u. 6, s. -M9 ; F. G. Short, Awer. Chemical Journ., April, 1887, p. 100 ; 

 Morse APigott, lb., April, 1887, p. 108 ; F. A. Woll, lb., February, 1887, p. 60 ; Morse and Burton, 

 lb., June, 1887, p. 222 ; lb., July, 1888, p. 322. 



