COMPOSITION OF HUMAN MILK. 373 



acid upon the milk-globules, to indicate the existence of a memhrane. This deduction, 

 however, is not justifiable. Acetic acid readily coagulates the caseine, a principle which 

 is most efficient in maintaining the fat in its peculiar condition. The coagulating caseine 

 then presses upon the globules, and produces, in this way, all the changes in form that 

 have been observed. 



Most of the other arguments in favor of the existence of a membrane have no support 

 from direct observation, and consequently they do not demand special consideration; 

 while all the facts which we have been able to find relating to this subject go to show 

 that the fatty matters in the milk are in the condition of a simple emulsion. The precise 

 condition, however, of the fluid immediately surrounding the globules is not fully under- 

 stood. Certain of the constituents of fluids capable of forming emulsive mixtures with 

 liquid fats may form a coating of excessive tenuity immediately around the globules, but 

 they never constitute distinct membranes capable of resisting the action of solvents upon 

 the fats; and, in the case of the milk, they do not prevent the mechanical union of the 

 globules into masses, as occurs in the process of churning. Milk-globules less than ^Vs of 

 an inch in diameter present under the microscope that peculiar oscillating motion known 

 as the Brownian movement. This is arrested on the addition of acetic acid, by coagula- 

 tion of the caseine. From these facts, it is evident that the milk-globules are composed 

 simply of fat in the form of a fine emulsion. They are not true anatomical elements, 

 originating by a process of genesis in a blastema, undergoing physiological decay, and ca- 

 pable of self-regeneration from materials furnished by the menstruum in which they are 

 suspended, like the blood-corpuscles or leucocytes. They are simply elements of secretion. 



Composition of the Milk. "We do not propose, in treating of the composition of the 

 milk, to consider the various methods of analysis which have been employed by different 

 chemists. The only constituent that has ever presented much difficulty in the estimation 

 of its quantity is caseine ; but the various processes now employed for its extraction have 

 led to nearly identical results. The following table, compiled by Eobin from the analy- 

 ses of various chemists, gives the constituents of human milk : 



Composition of Human Milk. 



Water 902-717 to 863-149 



Caseine (desiccated) 29-000 " 39*000 



Lacto-proteine I'OOO " 2-770 



Albumen traces " 0-880 



rMargarine 17'000 " 26-840 



Butter, 25 to 38 -I Oleine 7'600 " H'400 



[fiutyrine, caprine, caproine, capriline 0*500 " 0'760 



Sugar of milk (lactine, or lactose) 37'000 " 49-000 



Lactafe of soda(?) 0-420 " 0-450 



Chloride of sodium 0'240 " 0'340 



Chloride of potassium 1-440 " 1'830 



Carbonate of soda 0-053 " 0'056 



Carbonate of lime 0-069 " 0-070 



Phosphate of lime of the bones 2-310 " 3'440 



Phosphate of magnesia 0'420 " 0'640 



Phosphate of soda 0-225 " 0-230 



Phosphate of iron (?) 0-032 " 0-070 



Sulphate of soda 0-074 " 0'075 



Sulphate of potassa traces. 



( Oxygen 1'29 } 1,000-000 1,000'000 



Gases in solution < Nitrogen 12-17 > 30 parts per 1,000 in volume. (Hoppe.) 



( Carbonic acid. 16 '54 ) 



