NUTRITION 



ly, we have the very interesting pathogenetic bacteria 

 which cause the most dangerous diseases by the secretion 

 of special poisons — toxins — festering, small-pox, teta- 

 nus, diphtheria, typus, tuberculosis, cholera, etc. On ac- 

 count of their great practical importance, these bacteria 

 have of late been taken over by a special branch of biol- 

 ogy, bacteriology. But only a few of the many experts 

 in this department have pointed out the extreme theo- 

 retical significance which these zoomonera have for the 

 important questions of general biology. These struct- 

 ureless plasma bodies show unmistakably that their 

 vital activity is a purely chemical phenomenon. Their 

 great variety proves how manifold and complicated must 

 be the molecular composition of the plasm, even in these 

 simplest organisms. 



The unicellular protophyta exhibit the same form of 

 metabolism and plasmodomism as the familiar green 

 cells of the tissue-plants ; but in most of the protozoa we 

 find special features of nutrition and plasmophagy. The 

 great class of the rhizopods is distinguished by the fact 

 that their naked plasma body can take in ready-formed 

 solid food at any point of its surface. On the other 

 hand, most of the infusoria have a definite mouth-open- 

 ing in the outer wall of their unicellular body, and some- 

 times a gullet-tube as well. Besides this cell-mouth 

 {cytostoma) we usually find also a second opening for 

 the discharge of indigestible matter, a cell-anus (cyto- 

 pyge). 



Metabolism in the tissue plants (metaphyta) forms a 

 long gradation from very simple to very complicated 

 arrangements. The lowest and oldest thallophyta, es- 

 pecially the simplest algae, are not far removed from the 

 communities of protophyta, and, like these, are merely 

 definitely grouped colonies of cells. The social cells 

 which form their most rudimentary tissue are quite 

 homogeneous, with no differentiation beyond that of sex. 



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