180 PROTOZOA. 



animal which moved independently, while we, on the contrary, are 

 now acquainted with numerous plants and plant-embryos possessed 

 of the power of locomotion, and are indeed, on the strength of the 

 facts we have mentioned above, inclined to believe that contractility 

 is a general property of (living) organic matter. 



Those Bacteria* which we have mentioned are extremely small 

 rod-like, sometimes spiral, or spherical, bodies, which always abound in 

 decaying organic matter, and multiply so rapidly by transverse division 

 that, as Cohn has calculated, a single individual (150,000 millions of 

 which make up a milligram) may in forty-eight hours produce a mass 

 of half a kilogram, and with good feeding may in three days leave a 

 progeny of 7- million kilograms, at least if those conditions which the 

 calculation postulates ever actually occur. 



They are, however, not only attendant on processes of decomposi- 

 tion and decay, but are able to originate and keep up these and 

 similar processes, acting, like the yeast plants, as oxidising and 

 reducing ferments, taking in or giving out oxygen. Thus they 

 play a most important rdle, some occasioning ordinary putrefaction 

 (Bacterium termo), others the butyric (Bacillus butyris), and others 

 again the lactic and acetic fermentations. The so-called " mother of 

 vinegar " of the latter consists essentially of an organism resembling 

 Bacterium (Mycoderma aceti). 



To this fact, the Schizomycetes owe their high importance in 

 pathology, for they are found not only more or less constantly and 

 plentifully in the excretions and faeces of animals (diarrhoetic dis- 

 charges, purulent matter, alkaline urine, encrustations on the teeth, 

 &c.), but also in the juices and tissues of the body, which must there- 

 fore be correspondingly altered by them. Thus the splenic fever 

 of our domestic animals depends, as we now know with the greatest 

 certainty, on the presence and growth of Bacteria (Bacillus anthracis) 

 which infect the blood, 2 and which, on transference to man, may 



1 Of the voluminous literature on the subject of Bacteria I will only mention Cohn's 

 researches, " Beitrage zur Biologic der Pflanzen," Hefte ii., in., 1872 and 1873. 



2 Through the investigations of Koch and Cohn (lor., cit. ), we now know the whole life- 

 history of the usually motionless splenic fever Bacteria. As long as they are contained 

 in the living host, they remain unchanged, but in the blood or suitable juices of the dead 

 animal they grow out into a long unbranched thread, which develops numerous small 

 shining spores. After these have been carried into a living body, they give rise 

 to Bacteria again, which at once begin to divide. This transference may not take 

 place for a long time, for the spores are able, without loss of their reproductive capabilities, 

 to lie dried up for years, or to remain whole months in putrefying fluids, or even to en- 

 dure alternately damp and dry environment. The transmission is probably effected by 

 external contact, the spores being carried into wounds, perhaps along with dust. No in- 

 fection is possible internally from the stomach. If the blood and tissues of the dead 

 animal are rapidly dried, so that the Bacillus is unable to form spores, then the possibility 

 uf infection only lasts a few weeks. 



