18 DIRECTOR’S REPORT OF THE 
A currant rust new to America.—In September, 1906, the Station 
currant plantation was found to be abundantly infested with a 
leaf-rust fungus (Cronartium ribicola) which, with one possible 
exception, has not been found previously anywhere in America. 
In Europe it has been known for fifty years and is there wide- 
spread. As a currant disease it is not much to be feared. The 
chief danger from it lies in its effect on white pines. In one of 
its stages the fungus attacks the trunks and branches of the white 
pine producing a destructive disease. It would be unfortunate if 
this disease should become scattered throughout America. With- 
out doubt it is a recent importation from Europe, but just how it 
came to the Station grounds is not known. In order to stamp out 
the disease, if possible, every currant and gooseberry bush on the 
Station grounds has been destroyed. An account of this currant 
rust appears in Technical Bulletin No. 2. 
DEPARTMENT OF CHEMISTRY. 
The action of acids on casein when no solution occurs.—This 
work has for its object to gain information as to whether casein 
forms an insoluble compound with acids, as in the case of milk 
curdled by natural souring. The question has been at issue for over 
fifty years and is of importance as having a practical relation to 
certain dairy problems. The methods that have been commonly 
employed in studying this question are found to be unreliable 
except under special conditions, which have not been appreciated 
heretofore. A new and reliable method was employed, by which 
the amount of acid taken up by casein is measured by means of 
changes in the electrical conductivity of the solutions used. It is 
shown that casein has the power of taking up acids, but the action 
appears to be more like physical adsorption than like chemical com- 
-ination. Casein takes up different amounts of acid according to 
the time of contact, concentration of acid, etc. It takes up different 
acids in different amounts characteristic for each acid. The work 
was carried on with hydrochloric, lactic, acetic and sulphuric acids, 
of varying degrees of concentration and at several different tem- 
peratures. . ; 
The accuracy of phenolphthalein as an indicator in measuring the 
acidity) of casein.—Different indicators show different amounts of 
