110 MASS. EXPERIMENT STATION BULLETIN 175. 



However, these organisms were always mixed with certain bodies probably 

 of a protein nature, and Noguchi, himself, so far has been unable to state 

 absolutely which may be the active agent, although he naturally infers 

 from his inoculation experiments that the organisms found must be the 

 causative agent owing to the extreme infectious character of the disease. 

 He, however, states that it is not absolutely clear to him whether the 

 organism alone or a combination of this organism with the bodies found 

 in culture associated with it are capable of producing infection. He 

 does state, however, that in the case of animal pathology no such 

 symbiotic relationship has so far been observed. From the character of 

 his statement, however, it is clearly indicated that he does not preclude 

 the possibihty of such a condition arising. 



Probable Character of the Causal Agent. 



The question as to the exact character of the causal agent of mosaic 

 disease has been an extremely interesting one to investigators, and studies 

 on this phase of the problem have narrowed the field by the eUmination 

 from consideration of fungi and bacteria, as has previously been shown 

 not only in this work, but also by many other investigators. This also 

 precludes the presence of a virus or a toxin resultant from the activities 

 of such organisms. 



This leaves, then, for consideration as the causal agent an "ultrami- 

 croscopic" or "invisible" organism and the enzjonic activities in their 

 fullest conception. The reactions of the so-called "ultramicroscopic" 

 organisms are little known at present, and about the only grounds for 

 admitting of such a class of organisms is the infection factor, and possibly 

 reproduction to a certain extent. We do know, however, many reactions 

 of the class of substances called enzjones and toxins, but fundamentally 

 the differentiation of the three above mentioned is difficult, and is per- 

 haps in many cases impossible. Working with filtered sap from mosaic- 

 diseased plants, we get the following results in comparison with reactions 

 of some of the so-called "ultramicroscopic" organisms and toxins. 



Temperature. — The sap containing the causal agent of mosaic disease 

 becomes non-infectious; in other words, becomes inactive when heated 

 to about 80° C. for a short time. It is reported that ultramicroscopic 

 organisms and toxins are killed or rendered inactive, respectively, by 

 exposure to heat for any length of time at temperatures somewhat below 

 100° C. Enzymes are also rendered inactive at temperatures somewhat 

 below 100° C. All three react practically alike as regards temperature. 

 The causal agent in mosaic sap, as maj^ be seen, is also rendered inactive 

 at temperatures below 100° C. 



Size. — As to size, nothing can be definitely stated, but it is a fact that 

 the ultramicroscopic organisms, enzj^mes and toxins must have a diameter 

 of less than .1 //, otherwise they would become visible under the higher 

 powers of the microscope. In no case has it been possible to demonstrate 

 the presence of organisms under even the highest powers available. 



