no GEOGRAPHIC DISTRIBrTIOX OF nCBOXIC PLAGI'lC 



reference to its extension in America and the more enlightened conn- 

 tries of Europe. 



I have already referred to the fact that rats are suscei)tible to in- 

 fection by the plague bacillus. During the epidemic prevalence of 

 the disease these animals die in large numbers, and there is good rea- 

 son to believe that they ])lay an important part in the propagation of 

 the malady. It has been suggested that infection may be carried 

 from rats to man through the agency of fleas, which swarm upon these 

 rodents and desert them when the}' die. Plague bacilli have been 

 found in the intestinal contents of the flea, and it is said that when 

 an infected rat is freed from these parasites it cannot communicate 

 the disease by association with healthv rats. There is nothing im- 

 probable in the view that the flea may act as an intermediate host 

 for the plague bacillus and pla}^ an important role in the proi)agation 

 of the disease under consideration. In this connection it ma}^ ))e 

 well to recall the fact that the mosquito has been demonstrated to 

 serve as an intermediate host for the malarial ])arasite, and to phw 

 an im})ortant part in the communication of malarial diseases to man ; 

 also that the tick is tiie intermediate host of the i>arasite which is the 

 cause of an infectious disease of cattle known as Texas fever. 



In a recent paper Professor Galli-Valerio, of the Universit}' of Law- 

 sanne, combats the idea that the flea which is parasitic upon the rat 

 can be instrumental in conveying the infection of bubonic plague to 

 man. In experiments n)ade upon himself he was unable to obtain 

 any evidence that this Ilea (Typhlojisylla musculi) will remain upon 

 the body of a man unless under compulsion, or that it will puncture 

 the skin of a man. Pie admits, however, the i)ossibilit3' that plague 

 might be transmitted from man to man by the well-known domestic 

 flea (Palex irritdus). 



During the past two or three 3'ears a number of prominent bacte- 

 riologists have been engaged in researches relating to the jn*evention 

 and care of bubonic plague b}'' means of an antitoxic serum obtained 

 b}^ the same method and in accordance with the same fundamental 

 scientific principle as in the case of the antitoxic serum which is now 

 so successfully employed in the treatment of diphtheria. The ex- 

 periments thus far made have apparently been attended with a con- 

 siderable degree of success. Professor Calmette reports that the serum 

 of Yersin prepared at the Pasteur Institute, in Paris, proved to be 

 curative in a considerable proportion of the cases treated during the 

 recent outbreak at Oporto, and that protective inocnlations conferred 



