44 MEDICINE 



exact knowledge of the clinical phenomena of disease, of morbid 

 anatomy, of physiology, and of physiologic chemistry than would 

 have been possible without it. 



Transmission of Infection 



The knowledge of the cause of disease has led to a study of the 

 life-history of infective organisms outside of as well as in the animal 

 body. The mode of propagation, the means of transmission of in- 

 fective microorganism, by fomites and other agents, has become 

 known. The rdle of insects which infect animals play, as defin- 

 itive or intermediate hosts, has been studied and proved. The 

 discovery of Manson of the transmission of Filaria sanguinis hominis 

 by the mosquito was of vast importance as a suggestion of the 

 mosquito as a definitive host in malaria. The investigations of 

 Manson, Ross, Celli, Grassi, Dionise, Marchiafava, Bignami, Koch, 

 and others have made our knowledge of malaria exact. With the 

 microscope we may now not only recognize malaria and differentiate 

 it from the other infective fevers, but we may also at the same time 

 recognize by an examination of the blood the type of malarial in- 

 fection and foretell its course. Not only may we recognize the dis- 

 ease definitely and apply the drug treatment more rationally, but 

 the knowledge of the means of its transmission from man to man 

 enables us to apply preventive measures which are of the greatest 

 importance from a commercial as well as from a humanitarian 

 point of view. The recognition of the r61e of the mosquito in malaria 

 has been, furthermore, a stimulus to the study of the same insect 

 in relation to other infections. 



The brilliant research work of Reed and Carroll in 1900 in Cuba, 

 by which they proved that the mosquito of the genus stegomya 

 is the sole means of the transmission of yellow fever from man to 

 man, is of great importance as a scientific fact. The influence of this 

 discovery upon mankind, as a prophylactic against a disease which 

 has killed multitudes, is wonderful. 



Hardly less important is the fact that the Bacillus pestis may 

 infect fleas and these in turn infect rats, mice, and man. It is im- 

 portant, too, to know that pests like the house-fly may be carriers 

 of infective bacteria from refuse filth to kitchens and tables and con- 

 taminate food, and thus infect u swith typhoid fever, cholera, and 

 perhaps other diseases which are propagated by filth. 



The study of bacteria in the laboratory and hi the blood tissues 

 of infected animals has led to the discovery of the means by which 

 bacteria disturb the animal economy and produce phenomena 

 expressive of disease. The fact that the blood and tissues of infected 

 animals contained a toxin which could also be isolated from pure 



