Disease Transmission and Mans Resistance 297 



spirits due to an over-abundance of this humor. PJilegmatic, which 

 today means a shiggish, indifferent reaction, originally indicated a 

 disproportionate amount of phlegm. 



PYTHOGENIC THEORY OF DISEASE 



Dirt and filth, according to this theory, was the cause of disease, 

 especially typhoid fever. Decaying vegetation and animal matter 

 provided an excellent breeding ground for disease. This was pure 

 speculation with no scientific evidence to back it up when it was 

 originally proposed. 



THE GERM THEORY OF DISEASE 

 The belief that sub-visible organisms were the cause of much 

 of man's misery was postulated early in the nineteenth century, 

 when a few poorly conducted experiments were carried out with 

 no conclusive findings. Jacob Henle, a pathologist, advocated in 

 1840 that more careful investigations be conducted to prove or to 

 disprove this germ theory. If germs really cause disease, Henle 

 believed that they should be found in infected tissue, they should 

 be isolated from all other living matter, and when these isolates are 

 injected into animals, the germs should cause disease. Robert 

 Koch, who is usually given credit for the postulates he put forth to 

 prove the germ theory of disease, drew rather heavily on Henle's 

 proposals. This theoiy was not a sudden inspiration; it was the 

 result of the contributions of a number of workers, including 

 Leeuwenhoek, Fracastorius, and Plenciz. But until Koch had pro- 

 vided scientific proof through practical application of his postulates, 

 the germ theory of disease was not accepted. 



MODES OF DISEASE TRANSMISSION AND 

 PORTALS OF ENTRY 



Leaders in the field of public health frequently teach that 

 transmissible disease can often be attributed to one of the four F's: 

 flies, fingers, fomites, or food. To this list might be added droplet 

 infection and direct contact with infected persons and animals. 



