MATERIAL TRANSFORMATIONS IN THE PLANT 1 67 



worthy of note. These poisons may be effective as accelerators of material 

 exchange. According to Votchal,' solanin, which is a very poisonous alka- 

 loid, is formed in various parts of the potato tuber, especially during the period 

 of active growth. When the tuber is wounded a considerable amount of the 

 solanin accumulates in the neighborhood of the wound. It will be shown later 

 that, respiration, as well as other metabolic processes, is increased by injury 

 of plant tissues. Solanin thus seems to be a stimulant that increases metabolism 

 in wounded regions. 



Extremely active poisons are formed by bacteria. These organisms not 

 only destroy dead bodies, but many of them infest even living plants and ani- 

 mals, thus giving rise to various infectious diseases. They are the so-called 

 pathogenic forms. Bacillus tetani, the form that produces the disease known 

 as tetanus or lockjaw, is a typical example of the anaerobic pathogenic bacteria, 

 which develop only in the absence of oxygen. Many other pathogenic bacteria 

 are aerobic, however, and attain their full development only in the presence of 

 oxygen. Bacillus anthracis, which produces splenic fever, belongs in the latter 

 ■group. It was by the study of anthrax that Pasteur first made the discovery 

 that infectious diseases are caused and propagated by bacteria. It had long 

 been known that many bacteria are present in the blood of animals suffering 

 from splenic fever. Pasteur placed a drop of such blood in broth and obtained 

 an abundant development of bacteria. Re-inoculations were made, from the 

 first culture to a second, from the second to a third, etc., and the twentieth 

 culture was still capable of producing the disease when an animal was infected 

 with the Uquid. Pasteur deserves credit also for working out the method of 

 immunization by vaccination. In 1879 he began his work on the bacillus of 

 chicken cholera. Pmre cultures of this organism proved to have become greatly 

 weakened by standing in a thermostat during the summer; inoculation there- 

 from produced only a local effect and failed to cause the death of the fowl. It 

 also became evident that subsequent inoculation with extremely virulent, fresh 

 cultures was without fatal effect if the fowls had previously been inoculated 

 with the weakened culture. Generahzing from these observations, Pasteur 

 arrived at vaccination as a protection against anthrax. He found that the 

 virulence of the anthrax bacillus becomes weakened under the influence of bigh 

 temperature, gradually losing its poisonous properties at from 42 to 43°C. 

 Animals inoculated with such weakened cultures endure this inoculation, and 

 are then no longer susceptible to injury from inoculation with stronger cultures; 

 they are thus protected against anthrax. This leads to the supposition that 

 toxins are neutraUzed by antitoxins that are produced in the animal tissues. 

 A number of such antitoxins have been actually isolated. Vaccination protects 

 against infection, but after the disease is already developed it may be controlled 

 by direct injection of antitoxin. As is well known, diphtheria is combated by 

 means of diphtheria antitoxin, which is obtained from the blood serum of horses 



' Votchal, E., Zur Frage von der Verbreitung, Vertheilung urid RoUe des Solanins in den Pflanzen. H. 

 Das Geschick des Solanins in der Pflanze and seine Bedeutung far das Leben derselben. [Title in 

 Russian and German, article in Russian.] Trav. Boo. Nat. Univ. Imp. Kazan. 195: 1-74- 1889. Clau- 

 triau, G., Nature et signification des alcoloides vfig^taux. Rec. Inst. Bot. Bruxelle3;iS : 1-87. 1902. 



