40 Biological, Chemical and Physical Characteristics of Milk. 



Although the milk globules cannot be entirely freed from proteids by washing 

 (covering the milk with water and allowing the separation of fat), the demonstration 

 of the remains of proteids cannot be considered as proof of an actual "haptogen mem- 

 brane" which must be broken down during the butter-making process, in order to make 

 possible the flowing together of the milk fat, but it does constitute a proof that rem- 

 nants of proteids, even after the most careful washing of the cream, remain around 

 the fat globules. At least it has never been possible to demonstrate membranes of the 

 fat globules, neither in boiled milk, in which during continuous heating larger fat 

 clumps develop, nor in fat extractions (Soxhlet, Quincke, Morres). 



Milk sugar is also a specific substance of milk. It is formed 

 in the gland and is found only in its secretion. If sucking is in- 

 terrupted, it may be present in the urine, from which it immedi- 

 ately disappears upon amputation of the lactating gland, or it may 

 not appear at all when the gland is amputated before the appear- 

 ance of lactation (Sinet, Magnus-Levy, Zuntz). After the com- 

 plete removal of the gland in goats and cows, however, a temporary 

 hyperglycosemia and glycosuria appear. If parts of the gland 

 remain, lactosuria results. 



After the injection of glucose, lactose appears in the urine 

 (Porcher), likewise after the ingestion of large quantities of dex- 

 trose. Since the blood in the mammary vein before parturition 

 and during lactation contains considerably less glucose than 

 the blood of the jugular vein (Kaufman and Lagne), it may be 

 accepted that glucose has been utilized in the gland, and further 

 that glucose is the material from the constituents of which the lac- 

 tose is formed in the gland. 



Of the various salts milk contains compounds of potassium, 

 calcium, magnesium, iron, traces of manganese, aluminum, phos- 

 phoric acid, hydrochloric acid, carbonic acid, sulphuric acid, citric 

 acid, fluorine and iodine. 



Carbonic acid, oxygen and nitrogen have been demonstrated as 

 gases in the milk. 



Besides these substances, lecithin, cholesterine and coloring 

 matter are present in the milk, besides ferments and substances 

 which are collected as residual substances ; these have been pre- 

 viously mentioned. 



Baudnitz and Grimmer have recently published compiled arti- 

 cles relative to the individual constituents and chemical properties 

 of milk which contain the collected material of many experimental 

 results, and at the same time show how much is still unsettled in 

 regard to the composition of milk and the characteristics of the 

 substances which it contains. 



Certain physical characteristics of milk correspond to its 

 chemical condition. These adjust themselves according to the pro- 

 portion of the various constituents, and to the conditions attend- 

 ing the mixing of the different component parts. 



The appearance of the milk is influenced by the suspended 

 casein and the proportion of fat. Skimmed milk, which is almost 

 free from fat constitutes a non-transparent, somewhat bluish fluid, 

 as compared with the whitish yellow color of whole milk. The ad- 



