COMMUNICABLE DISEASES. 215 



medicinal purpose should be prohibited as it may be the means of starting 

 an epidemic of cholera in the United States. 



Fortunately the cholera bacillus is easily killed by heat, disinfectants, and 

 by drying. The temperature of boiling water kills it in five minutes. In 

 water it may retain its vitality for a long time. Furthermore, it is not a strict 

 (obligative) parasite and may multiply outside of the body under favorable 

 conditions. Flies carry the infection from cholera stools to articles of food. 



Haffkine's attenuated cholera bacterin has been employed successfully 

 as a prophylactic. The method of use consists first in the hypodermic in- 

 jection of a weak virus, that is, cultures attenuated by long cultivation at a 

 high temperature (39 C.), and following this later, in five days, with a 

 virulent culture. More recently Kolle has used cultures killed by heating 

 for one hour at 58 C., which has given good results in numerous tests made 

 during a cholera epidemic in Japan. Pfeiffer and others have experimented 

 extensively with cholera-immune serum and have demonstrated that this 

 has marked lytic properties. The cholera bacilli when placed into the serum 

 first lose motility, then swell up into coccus-like forms and finally dissolve. 

 This property is said to be due to two substances, one found in normal serum 

 and the other found in immune serum. Neither substance alone can de- 

 stroy the cholera bacilli but the two acting together are strongly bacterio- 

 lytic. The immunity produced by the Haffkine and Kolle bacterins is 

 temporary only. 



J. Yellow Fever. This highly infectious, but in no wise contagious, 

 disease is peculiar to tropical and subtropical countries. The primary 

 cause is as yet unknown but it is supposed to be a protozoan. The sole 

 carrier of the infection is a mosquito, Stegomyia calopus. The disease has 

 been highly epidemical in the southern states but since the discovery of the 

 part played by the mosquito the mortality rate has been lowered to a marked 

 degree. In fact the disease is now under complete control. No Stegomyia 

 mosquitos, no yellow fever. 



It had been observed for a long time that a frost checked the disease at 

 once, which as is now known, was due to the fact that the frost killed the 

 carriers of the infection. In a general way the statements made under 

 malaria prophylaxis also apply here. Caucasians, especially those not 

 acclimated in the yellow-fever countries, are very susceptible to the disease; 

 Negroes and Latin races are far less susceptible. 



K. Pellagra. Pellagra is a disease which has created great havoc in 

 Italy and other Eastern countries, and which first appeared in the United 

 States about 1907. It spread very rapidly and up to 1911 numerous cases 

 have been reported from the Southeastern United States and from Illinois, 

 with a few scattering cases from Kansas, Virginia, Pennsylvania, New 

 York, Massachusetts, California and other states. The disease is said to 



