24 THE PRESIDENTIAL ADDRESS. 
new era in its study has been opened up by the work of Whittingham and 
Rook, who have learned how to handle, breed, and keep sand-flies in cap- 
tivity, and have shown that the virus is transmitted from generation to 
generation of flies without intervening passage through man or other higher 
animal. The knowledge of the life history of the flies will no doubt lead 
in due course to the suppression of the disease. 
Another type of invertebrate vector is the Kedani mite, Trombicula 
akamushi, which transmits the virus of Japanese river-fever to man from 
wild animals. The dangerous character of this disease (‘Tsutsugamushi) 
and the minute size of the mite together have presented great difficulties 
to the Japanese investigators. Protection from the mite by special 
clothing and bathing after exposure to risk of infection are at present the 
most hopeful methods of prophylaxis. 
Antitoxie sera have also been used with some measure of success in 
the prevention of diseases of this group. Degkwitz and others in 
Germany are reported to have been very successful in protecting 
children from measles and scarlet fever by injecting them with a small 
quantity of serum from convalescent patients. This method has also 
been found very useful under suitable conditions to protect cattle from 
foot-and-mouth disease. 
But far more hopeful than protection by serum alone is the use of a 
vaccine to produce a lasting immunity, combined with antitoxin to prevent 
the vaccine from producing unpleasant results—the so-called toxin-anti- 
toxin method. Most of the diseases for which this method of prophylaxis 
has proved valuable have been diseases of animals, such as pleuro-pneumonia 
of cattle, rinderpest, and foot-and-mouth disease ; but quite recently the 
method of Dick, of Chicago, in scarlet fever has been supported by a number 
of observations. The system of testing and producing immunity is planned 
on the same lines as the Schick method for diphtheria. 
DIETETIC DEFICIENCIES.—DEFICIENCY DISEASES. 
The preceding account is but a short and meagre history of the mar- 
vellous advance which has been made in the prevention of infectious 
diseases in our times, an advance due in great part to the work of two 
men, Pasteur the Frenchman and Koch the German; those who have 
come after them have merely followed in their footsteps, been their 
disciples. 
Time will not permit even to touch upon the advances made in the pre- 
vention of other important diseases, such as the surgical infections and 
