MAMMARY SECRETION. 633 



removed to relieve the pressure within, otherwise it is apt to be forced out, with 

 consequent loss of material. Lay the tube on its side for a few minutes and then 

 shake it again ; add one cubic centimeter of ordinary ammonia diluted with about 

 its volume of water, and mix as before by shaking ; then add ten cubic centimeters 

 of 80 per cent, alcohol and mix again thoroughly by moderate shaking, holding 

 the tube from time to time in an inverted position. 



Now, put the tube in water kept at 40° to 45° until the ether-fat solution sepa- 

 rates ; this separation may be hastened by transferring the tube to cold water 

 after it has stood in the warm water for a few minutes, and then returning it to 

 the warm water. Finally, transfer the tube to water at 20° C, and as the level of 

 the liquid falls in the stem by contraction of the main body of it in the bulb, 

 gently tap the side of the tube below the ether-fat solution to dislodge any flakes 

 of solid matter that may adhere to the side. The readings are to be taken from 

 the lowest part of the surface meniscus to the line of separation between the ether- 

 fat solution and the liquid below it. 



The following table gives the percentages of fat corresponding to each tenth 

 of a cubic centimeter of ether-fat solution down to one cubic centimeter, and for 

 each twentieth of a cubic centimeter thereafter : — 



Reading. 



Per Cent, of Fat. 



Reading. 



Per Cent, of Fat. 



3.0. 



1. 



13.5 . 



3.51 



4.0. 



1.13 



14.0 . 



3.63 



50. 



. 1.47 



14.5 . 



3.75 



6.0 . 



. 1.71 



15.0. 



3.87 



7.0. 



1.95 



15.5 . 



4.00 



8.0. 



2.19 



16.0. 



4.13 



9.0. 



2.43 



16.5 . 



4.26 



10.0 . 



. 2.67 



17.0. 



4.39 



10.5. 



. 2.79 



17.5. 



4.52 



11.0. 



2.91 



18.0. 



4.65 



11.5. 



3.03 



18.5 . 



4.78 



12.0. 



3.15 



19.0. 



5.01 



12 5. 



. 3.27 



19.5. 



5.14 



13.0. . . 3.39 20.0. 5.27 



This method has been applied with fairly satisfactory results to the milk of a 

 herd of cows receiving bran and cotton-seed meal in their rations, the objection 

 to the unreliability of this method under these circumstances being overcome by 

 the use of the ammonia. Various other forms of lactoscope are used, depending 

 on the property that the opacity of milk varies with and is proportional to the 

 amounts of fats present. Skimmed milk contains smaller fat-globules than intact 

 milk, and this causes a greater cloudiness in proportion to the amount of fat pres- 

 ent than the large ones, and, hence, the application of this test to skimmed milk 

 would give a higher percentage of fat than is actually present. 



For the quantitative estimation of the different milk-constituents the following 

 methods, taken from Charles's "Physiological and Pathological Chemistry," are 

 the simplest and require the least apparatus : — 



1. The Solids— (j.) To ten grammes dry sand or powdered gypsum add five 

 cubic centimeters milk, then dry the mixture for a long time at 100° until the 

 weight is constant. The increase in weight is equal to the solids in five cubic 

 centimeters milk. Suppose this to be =0 5 gramme, then one hundred cubic 

 centimeters milk contain ten grammes, or 10 per cent, solids (Baumhauer). 



Instead of five cubic centimeters, ten grammes of milk and twenty grammes 

 of dry sea-sand may be weighed in a tared capsule of about fifty cubic centimeters, 

 and evaporated at 100° until the weight is constant. When quite cold, the cap- 

 sule, with its contents, is weighed in a desiccator over sulphuric acid. 



(ij.) Place a little milk in a platinum capsule, and, having weighed it, add a 

 few drops of alcohol or acetic acid ; evaporate over a water-bath, dividing the 

 coagulum against the sides of the dish, and dry it at 100° to 110° until the weight 

 is constant. It is generally completed in six hours (Gerber). Cover carefully 

 before weighing, as the residue is very hygroscopic. , 



The total solids should not, as a rule, be much less than 11.5 per cent. ; cows' 

 milk, for example, varies between 10.5 and 15 per cent. ; less than this indicates 

 dilution. 



2. The Butter.— Q.) Shake the milk well, and to twenty cubic centimeters of 

 it add twenty cubic centimeters of a 10 per cent, caustic potash solution and 

 then some ether (sixty to one hundred cubic centimeters), and agitate vigorously 



