MILK 319 



next in importance to casein, closely resemble serum albumin and 

 serum globulin in their general properties. 



Butter (milk fat) consists in large part of olein and palmitin. 

 Stearin, butyrin, caproin and traces of other fats are also present. 

 When butter becomes rancid through the cleavage of certain of its 

 constituent fats by bacteria the odors of caproic and butyric acids are 

 in evidence. 



The pigment of the fat of cow's milk is made, up of carotin and 

 xanthophylls. The principal pigment is carotin, an unsaturated 

 hydrocarbon pigment which is widely distributed in plants. 1 The 

 pigment of the fat of human milk is made up of carotin and xantho- 

 phylls in about equal proportions. Carotin is also probably the 

 pigment of human fat. The pigment of body fat, blood serum, corpus 

 luteum and skin secretions of the cow is principally carotin. 



Colostrum is the name given to the product of the mammary gland 

 secreted for a short time before parturition and during the early period 

 of lactation (see Fig. 103, page 315). It is yellowish in color, contains 

 more solid matter than ordinary milk, and has a higher specific gravity 

 (1.040-1.080). The most striking difference between colostrum and 

 ordinary milk is the high percentage of lactalbumin and lacto-globulin 

 in the former. This abnormality in the protein content is responsible 

 for the coagulation of colostrum upon boiling. 



Such enzymes as lipase, amylase, galactase, catalase, oxidases, 

 peroxidases, and reductases have been identified in milk, but not all of 

 them in milk of the same species of animal. 



Among the principal preservatives used in connection with milk are 

 formaldehyde, hydrogen peroxide, boric acid, borates, salicylic acid, 

 and salicylates. The use of milk preservatives is illegal in most states. 



EXPERIMENTS ON MILK 



1. Reaction. Test the reaction of fresh cow's milk to litmus, phenolphthalein 

 and Congo red. 



2. Biuret Test. Make the biuret test according to directions given on 

 page 98. 



3. Microscopical Examination. Examine fresh whole milk, skimmed or 

 centrifugated milk, and colostrum under the microscope. Compare the micro- 

 scopical appearance with Fig. 103, page 315. 



4. Specific Gravity. Determine the specific gravity of both whole and 

 skimmed milk (see page 324). Which possesses the higher specific gravity? 

 Explain why this is so. 



5. Film Formation. Place 10 c.c. of milk in a small beaker and boil a few 

 minutes. Note the formation of a film. Remove the film and heat again. Does 



1 Palmer and Eckles: Jour. Biol. Chem., 17, 191, 1914. 



