206 TWENTY-FIFTH ANNIVERSARY REPORT. 
at once completed, such as milling, salting, and putting in molds for 
pressing. 
While it has been generally supposed that the presence of some 
acid, presumably lactic acid, in the cheese-making process is, in 
some way or other, responsible for the most important changes 
taking place, such as the shrinking of the curd, the acquired ability 
to form strings on hot iron and the change in appearance and 
plasticity of curd, no one has ever been able to show in what 
way these changes were brought about by acids. It has been 
commonly supposed that the observed changes were purely physical 
in character and were not the result of chemical changes in the 
curd. We have studied more fully than has been done previously 
the real function of acids in relation to the important changes tak- 
ing place in cheese-curd during the cheddar process of cheese- 
making. 
I. ACTION OF LACTIC ACID UPON INORGANIC CONSTITUENTS OF MILK 
AND CURD. 
The first work of lactic acid appears to be its action upon some 
of the inorganic constituents of milk and curd, especially the cal- 
cium and phosphoric acid compounds. The phosphates at first 
present in cheese curd are insoluble. These are acted upon by 
lactic acid, forming soluble phosphates and calcium lactate. The 
main fact is that the calcium and phosphoric acid compounds of 
cheese-curd, which are insoluble at the start, gradually become 
soluble until about 80 per ct. of the calcium and all of the phos- 
phates appear in water solution. This change is due to the forma- 
tion of lactic acid and its action upon the phosphates of the cheese, 
changing insoluble into soluble phosphates and forming at the same 
time calcium lactate. The maximum amount of calcium is found 
in water solution at about the same time the phosphoric acid becomes 
entirely water-soluble. This appears to indicate that the water- 
soluble calcium present in cheese in its early history comes from 
j:organic combinations; namely insoluble phosphates, and not from 
the calcium combined with paracasein as calcium paracasein. 
2. CHANGES IN PROPERTIES OF CHEESE-CURD. 
After the curd is cut in the process of cheese-making and after 
heat is applied, the curd undergoes some marked changes. The 
pieces of curd gradually shrink in size, as the result of loss of whey, 
and become more firm in consistency. After the whey is removed 
