60 Transactions Tennessee Academy of Science 



Not many human diseases are caused by fungi, but a whole order 

 of fungi, the entomophthorales, are for the most part parasitic on 

 insects. The common Empusa muscae, a parasite of the house fly, 

 is a good example of the latter. Actinomycosis, lumpy jaw of cattle, 

 is one of the fungi known as pathogenic to man. The tumor-like 

 growths caused by this parasite of cattle and men have a striking 

 resemblance to fungus galls, or tumors, produced on plants. 



Bacteria as productive of plant disease, were first recognized by 

 Burrill, a veteran American plant pathologist, between 1877 and 

 1884 in the discovery of Bacillus amylovorus as the cause of pear 

 blight. This organism ordinarily gains access to the tissues of the 

 host through the blossoms. It is disseminated, as shown experi- 

 mentally by Waite, mostly by bees visiting the flowers for nectar. 

 It may be remarked, by the way, that this fact was brought out long 

 before we had heard of insects as carriers of human disease. 



Another and very different type of bacterial disease is the crown 

 gall. The aetiology of this disease for many years baffled investiga- 

 tors, and it was not until 1904 that Dr. Erwin F. Smith, of the United 

 States Department of Agriculture, almost accidentally found it due 

 to a bacterium, which he named Bacterium tumefaciens. He was at- 

 tempting to get cultures of microorganisms from the interior of a 

 tumor, and while he found several forms developing in his cultures, 

 none had proved to be pathogenic. Finally he happened to examine 

 some discarded Petri dishes in which some ager cultures had been 

 made from crown gall material, when he observed some newly 

 formed, pale yellow colonies. These proved to be the organism 

 producing the tumor, as shown by numerous cross inoculations 

 among various species of plants. A striking point in connection 

 with this organism is that it has rarely been found in preparations 

 of gall tissue. This is explained on the supposition that there is 

 here such a delicate balance between host and parasite that the 

 bacteria are disintegrated almost as rapidly as they are formed. 

 Dr. Smith has urged with a great deal of force the striking analogy 

 between crown gall of plants and cancer of the human body, and 

 one German investigator has gone so far as to attempt to show that 

 the same organism may be responsible for both diseases. Smitli 

 calls the crown gall a plant cancer and has shown that, after making 

 due allowance for the difference in anatomy and physiology of the 

 plant and animal, every symptom and observed fact in the one 

 case is true in ihc other, except that the causative organism has been 



