312 



FOUNDATIONS OF BIOLOGY 



chemical reactions are known to occur. Again, the spores 

 of other Bacteria can endure a temperature as high as 120 C. 

 for a short time. 



It is clear that the great majority of organisms are at the 

 mercy of environmental temperatures. This is true of all 

 except the higher Vertebrates, the Birds and Mammals. 

 These so-called warm-blooded, or HOMOTHERMAL, animals 

 possess a highly complex mechanism which maintains their 



1 



A B 



Flo. 160. Spore formation and germination in Bacteria. A, B, C, a 

 pair of rods forming spores, drawn at one hour intervals; D, a five-celled 

 rod, with three fully-formed spores, which was allowed to dry for several 

 days and then placed in a nutrient medium; E, F, the same spores at 

 one and three hours later; G, a pair of typical vegetative rods. (From 

 Sedgwick and Wilson, after De Bary.) 



body temperature practically constant; e.g., in Man at 37 C. 

 (98.6 F.). 



The heat regulatory mechanism represents, so to speak, 

 the culmination of the assembling and elaborating, during 

 Vertebrate evolution, of elements, the genesis of which is 

 found among the Fishes. In the Mammals it comprises 

 insulating material in the skin, a closed blood vascular 

 system, power of rapid oxidation, endocrinal and other 

 glandular products, evaporation surface of the lungs and 

 skin, 'trophic' and 'temperature' nerves, coordinating 

 centers, etc., the whole complex rendering its possessors 

 largely independent of the surrounding temperature and 

 making possible a carrying on of the various bodily functions 

 with such nicety as the life of these forms demands. 



