420 MILK AND MILK-PREPARATIONS. 



deny the presence of the casein-capsule ; according to them milk is a simple emul- 

 sion, permanently maintained as such by means of the colloid casein, which is 

 simply swollen in milk-plasma. The treatment of milk with potassium and ether 

 renders the casein of the plasma unfitted to maintain the emulsion of the milk 

 permanently. 



The fats of the milk- globules (human) are the triglycerids of stearic, palmitic 

 and oleic acids, in lesser amount of myristic, capric, caprylic, caproic and butyric 

 acids. In addition there are found traces of formic acid and cholesterin. 



By means of long-continued beating of milk (churning) , and even more readily 

 of cream, the fat of the milk-globules (after rupture of the casein-capsule) is ob- 

 tained as butter in coherent masses. Butter is soluble in alcohol and ether, and 

 is purified by melting at 60 C., or by washing with water at 40. On standing 

 in the air it becomes rancid, from the glycerin of the neutral butter-fats being 

 decomposed by the action of germs into acrolein and formic acid, which, with the 

 volatile fatty acids, give the odor. 



The milk-fluid (plasma lactis) is clear, somewhat opalescent and contains 

 proteids, chief among which is casein, together with a small amount of lact- 

 albumin and lacto globulin and the opalescent opalisin, a little nuclein, phospho- 

 carnic acid and a trace of diastatic ferment (in human milk) . 



Casein is retained in the filtration of milk by means of fresh animal membrane 

 or by means of clay cylinders. It can also be completely precipitated out of 

 human milk by means of saturation with magnesium sulphate, from cow's milk 

 by means of a little acetic acid. Quantitative Determination in Cow's Milk: 

 Twenty cubic centimeters of cow's milk are diluted with 60 cu. cm. of water, and 

 30 cu. cm. of a i in 1000 sulphuric-acid solution are added with stirring, precipi- 

 tating the casein of cow's milk. After five hours filtration is practised, the filter is 

 washed with water, twice with alcohol and fifteen times with ether, and it is then 

 dried and weighed. The casein can be completely precipitated by addition of 

 alum at a temperature of 37 C. Magnesium sulphate then precipitates the globu- 

 lin in the filtrate. Globulin and albumin together are precipitated from the filtrate 

 by means of tannic acid. 



The albumin in milk coagulates on boiling; in addition the free surface be- 

 comes covered with a skin of insoluble casein. 



The plasma contains, further, milk-sugar, a carbohydrate resembling dextrin, 

 lactic acid?, lecithin (if times as much as in cow's milk), urea, traces of kreatin, 

 kreatinin, xanthin-bodies (potassium sulphocyanid in cow's milk) ; sodium chlorid, 

 potassium chlorid, alkaline phosphates, calcium and magnesium sulphates, alkaline 

 carbonates and in addition traces of iron, metallic fluorids and silica, carbon dioxid, 

 nitrogen, oxygen and ammonia. Human milk contains numerous staphylococci. 



The curdling of milk consists of a coagulation of the casein. The latter is 

 combined in the milk with calcium phosphate, and is therefore soluble. Acids, 

 which remove the calcium phosphate from the casein, cause coagulation of the casein ; 

 lactic acid acts most readily in this connection, then hydrochloric, nitric, sulphuric, 

 acetic and phosphoric acids. Acetic and tartaric acids, when added in excess, re- 

 dissolve the precipitated casein. Human milk is not curdled by all acids, but only by 

 means of two or more drops of o.i per cent, hydrochloric or 2 per cent, acetic 

 acid. Heating above 130 C. coagulates the milk, acids being formed from milk- 

 sugar as a result of the action of heat and the contained casein becoming more 

 coagulable. The spontaneous curdling of milk after standing for some time, 

 especially in the heat, results from the formation of lactic acid by the bacillus 

 acidi lactici, which transforms the neutral alkaline phosphate into acid phosphate, 

 removes the calcium phosphate from the casein and thus precipitates it. The 

 sugar is transformed into lactic acid and carbon dioxid. The bacillus furnishes 

 the stimulation for this decomposition, while the casein of the milk is the actual 

 fermenting body. 



By means of the lab-ferment milk of alkaline reaction may be coagulated 

 (sweet whey) . This ferment decomposes the casein in the precipitated cheese and 

 the scanty but readily soluble whey-albumin. The lab-coagulation is then quite 

 different from the others. It takes place only when calcium-salts are dissolved 

 in the milk. If these are precipitated by means of potassium oxalate, the lab- 

 ferment no longer causes coagulation in the fluid; this latter, however, occurs 

 again as soon as calcium chlorid is added. 



Boiling (by destroying lower organisms) , sodium bicarbonate ( T Vo o) ammonia, 

 salicylic acid GfiW), also glycerin and ethereal oil of mustard, prevent spontaneous 

 coagulation. Fresh milk renders tincture of guaiac blue; boiled milk does not. 

 After standing for some time in the air milk gives off carbon dioxid and absorbs 



