PATHOGENIC OR NON-PATITOGENTC TO ANTMALS? 



89 



harbored by plants. Of those known to cause animal diseases none have ever 

 been found naturally present in plants, but some of them, such as the ty])lioid 

 bacillus, the anthrax organism, etc., have been shown to live for a number of 

 days or weeks when injected into various living plants, and in some instances have 

 been found to multiply a little in the vicinity of the wounds. In general, their life 

 IS short in such situations, they do not penetrate far into the tissues, and they are 



manifestly on the defensive. If they 

 can do no better when injected into 

 vegetable tissues in enormous c[uanti- 

 ties, it seems rather unlikely that under 

 ordinary natural conditions they woidd 

 find their way into plants so as to 

 make thenr dangerous for food. In 

 this connection the reader is referred 

 to Volume II, where this subject is 

 discussed more fully. More danger is 

 likely to result from pathogenic organ- 

 isms carried on the surface of plants, 

 especially on salads and fruits which 

 are irot cooked. In times of the gen- 

 eral prevalence of t)-phoid fever, chol- 

 era, or the bidionic plague, the writer 

 for one would certainly prefer to forego 

 salads and to eat only freslih' cooked 

 vegetables. The danger from such 

 foods in time of epidemics is very 

 great, especially in localities where 

 ditch-water is frequently sprinkled on 

 the vegetables to freshen them, c. g.^ 

 in parts of southern Italy. 



Most saproph)tes when injected 

 into living plants behave in the same 

 way as the animal parasites, /. c.^ they 

 either die at once or maintain a pre- 

 carious existence for some weeks in the vicinit}' of the wound and then succumb. 

 The writer has made many experiments, with negative results. The most extensive 

 published series of experiments are those of Zinsser (Jahrb. f wiss. ISot., 1897 ). 

 To get a particular disease, the parasite must be used and not some other organism. 

 This the writer has observed over and over again. This statement holds good with 

 plants the same as with animals. In case, however, of the less typical plant diseases 

 (soft rots) various members of a group of closely related organisms mav produce 

 essentially similar phenomena. This is paralleled, however, in certain of the less 

 typical animal diseases. 



Fig. 73.-: 



*FiG. 72. — Seedling svveet-corii plant cxtrudins w.iter from its leaf-tips. Most of the infections 

 by Bacterium Stewarti take place during this stage of growth, the bacteria passing down the leaf 

 through its vessels and entering the stem through the lower nodes. Natural size. 



