330 PEACTICAL PHYSIOLOGY 



precipitate in nitric acid and heat as before with ammonium molybdate 

 Show the presence of chlorides by means of silver nitrate test a 

 white precipitate insoluble in nitric acid, soluble in ammonia. 



EXPERIMENT X. THE DETECTION OF CALCIUM SALTS. To some 

 whey, freed from protein by boiling, add a few drops of a solution of 

 potassium oxalate a white haze of calcium oxalate results. 



IV. The Fats of Milk. Examine a thin film of milk under the 

 microscope, and note that the fat consists of small spherical bodies, 

 which are transparent and do not adhere to one another. 



The fat can be removed by shaking the milk with ether after the 

 addition to it of a few drops of weak NaOH solution. 



EXPERIMENT XL To about 5 c.c. of milk in a test tube add two 

 drops of caustic soda (20 %), and then about 5 c.c. of ether. Cover the 

 top of the tube with the thumb and shake the mixture, occasionally 

 lifting the thumb slightly to allow the vapour of ether to escape. The 

 ether will dissolve the fat, and the milk will become much less opaque. 

 By adding alkali, a certain amount of the caseinogen is changed in its 

 physical condition, so that the caseinogen films, which lie between 

 and thereby hold apart the fat globules, are diminished, and conse- 

 quently the fat globules are dissolved by ether. So long as they are 

 surrounded by caseinogen molecules they are not acted on by ether. 

 Not only alkalies, but also acids can effect this change. 



When the milk stands for some time, the fats, being specifically 

 lighter, rise to the surface to form the cream, and if this be mechanically 

 agitated it solidifies to form butter. Analysis of an ethereal extract of 

 milk shows that the fats are olein 40 %, palmitin 33 %, stearin 16 %, and 

 about 7 % of lower fatty acids, such as butyrin. There are minute 

 traces of lecithin and cholesterol. 



Colostrum. The milk which first appears during lactation is yellower 

 in colour and of higher specific gravity than that secreted later. On 

 boiling, it yields a distinct coagulum of albumin and globulin, and if 

 examined under the microscope it will be found to contain numerous 

 cells colostrum corpuscles in the protoplasm of which fat globules are 

 present. These cells are, in reality, secretory cells of the mammary 

 glands which have been extruded in the first portions of milk 



The Quantitative Determination of the various Bodies in Milk. 



The methods here described can be employed for other fluids besides milk. 



(1) The Percentage of Water. A weighed quantity of milk is mixed with 

 a weighed quantity of fine quartz sand, which has been previously heated to 

 redness and then cooled in a desiccator. The weight of the mixture is accurately 

 determined, and it is then placed in a hot air bath heated to 100 C. until all the 

 water has been driven off and the weight is constant. The amount of weight lost 

 corresponds to the amount of water which the sample of milk contains. 



