ORGANS OF THE ENERGIZING SYSTEM 79 



as the animal substances, yet on digestion plant and animal 

 proteins, etc., give much the same cleavage products. 



2JC. The Saprozoic and Saprophytic Modes. Many- 

 animals (tapeworms and other parasites) live in the bodies of 

 other animals. These internal parasites may have no trace of an 

 alimentary canal and may simply absorb nutriment from the blood, 

 lymph, or intestinal, or peritoneal fluids in which they are placed. 

 The whole external surface of the parasite may be such an absorb- 

 ent organ. It is probable that molluscs, etc., may also absorb 

 dissolved organic matter contained in the water currents that flow 

 through their mantle cavities. Deep sea fishes, etc., eat the ooze 

 that lies on the ocean bottom ; this ooze is supposed to consist 

 partly of the decomposing bodies of minute organisms that live in 

 the water of the ocean near the surface. Infusoria and other protists 

 live in " infusions," or liquids containing soluble organic matter. 



There are analogous plant organisms feeding in the same 

 essential way. In all cases what the saprozoic or saprophytic 

 organism feeds on is soluble organic matter absorbed via the 

 skin, gills or other external surfaces, or even by the mucous 

 membrane of the alimentary canal, as when a man drinks '* Oxo," 

 or " Bovril," or some such liquid food. In the wild state the 

 soluble organic matter comes from the decomposition of plant and 

 animal tissues. 



2yd. The Ambiguous Modes. The above distinctions are not 

 absolutely general, (i) Insectivorous plants can capture and 

 digest the bodies of insects although they also utilize CO 2 and OH 2 

 in the typical holophytic mode. (2) *' Plant-animals " (some 

 worms, the zooids of some corals and exceptional molluscs) have 

 green, chlorophyll — containing cells (" symbiotic algae ") in their 

 tissues and the latter cells can utilize CO 2 and OH 2 while the 

 animal can also feed in the typical holozoic mode. (3) Some 

 animals (molluscs and sponges and perhaps worms) can live on 

 dissolved organic matter while also capturing and ingesting food 

 organisms. 



zye. The Bacterial Modes (Bacteria may be regarded as 

 among the very primitive plants). They may be thus classified 

 — as regards nutrition : 



{i) The Prototrophic forms, 

 (a) Nitrifying Bacteria. These can, with either no organic 

 matter, or a bare minimal quantity, break down nitric into nitrous 



