106 MASS. EXPERIMENT STATION BULLETIN 175. 



activities of others; it was believed by the writer, with Woods and others, 

 that the disease might be physiological in nature, particularly in so far 

 as the causal agent, not being a Uving organism in the ordinary conception 

 of the word, was concerned. 



So Uttle is known about the action of the so-called ultramicroscopic 

 organisms that it is an open question in the writer's mind whether this 

 division should be the dumping ground for all infectious diseases about 

 the etiology of which little or nothing is known. 



It is conceivable that other causes, not organic in nature, may be able 

 to produce the manifestations of parasitism. Under this type of infection 

 would be included infectious diseases caused by enzjones or the resultant 

 product of the activities of a group of enzymes. 



Certain reactions of the juice from diseased plants tend to confirm this 

 view, and in the following pages are given the results obtained by the 

 writer and other investigators relating to the reactions of these juices 

 with various reagents. 



Drying. — It has been shown by various investigators that the dried 

 leaves of the mosaic-diseased plants retain their infectious quahties for 

 a long time. Beijerinck and Allard found that diseased leaves were capa- 

 ble of causing infection after being dried for periods of two years and 

 eighteen months, respectively. The writer has used material three years 

 old, and obtained infection in a great majority of cases. The results 

 obtained are given below. 



Table XII. — Air-dried Mosaic Leaves, finely ground and macerated with 

 Cold, Distilled Water. 



[Leaves (herbarium specimens) three years old.] 



Filtration. — The use of various filters such as the Chamberland, 

 Berkefeld and Kitasato types, as a means for the separation of bacteria 

 and other organisms in a fluid, has been widely adopted in recent years, 

 and more recently filters possessing different sized pores have been used 

 for differential diagnostic purposes in work on the so-called "ultramicro- 

 scopic" organisms, enzymes and toxins. While these methods are without 

 doubt of importance, it should always be borne in mind that to obtain 

 true filtration effects comparatively large volumes of the fluid should 



