CHARACTER OF THE TUMOR. 167 



pieces of tissue and that tissues so inserted would grow into a new 

 tumor, and in that period we were in precisely the same condition as 

 the animal pathologists of to-day, who reproduce mouse tumors and 

 similar malignant growths by introducing pieces of the diseased 

 tissue under the skin of healthy animals, but can not explain the 

 reason why. We did not then know that such plant tumors were 

 due to a specific organism, and a good many of us were very skeptical 

 as to the existence of a parasite, because after repeated careful 

 searches by a good many people no such organism had been demon- 

 strated in situ by means of the microscope, and the things which had 

 been plated out of such plant tumors and tested on healthy plants 

 had produced in them nothing comparable to the growth from which 

 they had been taken. Enough such experiments have been made 

 and by a sufficient number of persons to show that unless one knows 

 just how to set to work it is not at all easy to obtain the pathogenic 

 organism from crown-galls. As stated in the beginning of this 

 bulletin, we boggled away at the problem a couple of years before we 

 were certain by isolations and inoculations that we had in a particular 

 micro-organism the specific cause of the disease. Our troubles were 

 of various sorts. First of all the tumor tissue when it has reached 

 any considerable age is rapidly invaded by secondary organisms, i. e., 

 saprophytes, and on the plates these are the ones that we commonly 

 obtained. Isolation is also complicated by the fact that the organism 

 which is the cause of the disease is a rather sensitive one, i. e., fre- 

 quently is killed out quickly in the struggle with saprophytes. The 

 problem was further complicated by the fact that on standard +15 

 nutrient agar, which was our common substance for poured-plate 

 isolations, the initial growth of the bacteria taken directly from the 

 interior of the tumor and distributed in the agar plates is extremely 

 slow, so that often colonies visible to the naked eye are not seen 

 before the fifth or sixth day, and sometimes not until the tenth or 

 twelfth day or later. In other words, the saprophytes would come 

 up quickly and be studied and the overgrown plates discarded before 

 the right organism would appear at all. 



The writers also believe that the organism in the tumors either 

 multiplies very slowly or if growing at an ordinary rate is killed off 

 rather rapidly by the chemical reactions of the plant itself, or by the 

 ])y-products of its own growth. We have been led to this hypothesis 

 by several facts. First, it is not easy to obtain stained preparations 

 of the tumors in which the bacteria can be demonstrated. After six 

 years we have to show not a single good preparation. We get 

 numerous granules of the size of bacteria, and some of them of the 

 general outline, but so far with few exceptions none which take a 

 sharp stain leaving well-defined walls such as one looks for in order to 

 be reasonably certain that he has bacteria in his preparation and not 



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