39 
Composition of Albumen in 100 parts : — 
Carbon 53*5 
Hydrogen 7’0 
Nitrogen 15*5 
Oxygen . . 22-0 
Phosphorus 0*4 
Sulphur 1*6 
100-00 
Casein and animal albumen are remarkably similar in 
composition ; casein differs in not being coagulated by heat, 
and is precipitated by acetic acid. Certain animal sub- 
stances cause its coagulation, such as the dried stomach of 
the calf, known as rennet, used in the manufacture of 
cheese. 
When a thin film of milk is examined with the microscope, 
it is found to be a transparent fluid, in which are floating 
numerous transparent globules of fat ; these are surrounded 
by a thin pellicle, and when this pellicle is broken mechani- 
cally, as by churning, the fat is liberated and forms butter. 
The fluid part consists of casein, saccharine matter, and 
salts in solution. The proportion of these organic principles 
varies in different animals, and also in the same animal 
when fed under different conditions. Human milk usually 
contains a larger proportion of sugar than cow milk, and is 
coagulated with greater difficulty. It is well known that 
the secretion and quality of milk is influenced by the men- 
tal emotions. Milk as obtained in towns is frequently adul- 
terated, and as foreign matter would alter its microscopical 
characteristics, it was necessary to procure pure milk. One 
of our members, Mr. Kipping, kindly supplied me with a 
bottle of fresh drawn milk. The cow had calved about 
three months previously, and had been fed on grass, bran, 
and bean flour. This milk was examined soon after I re- 
ceived it, and was found to be very rich in oleaginous 
