278 



GENERAL PHYSIOLOGY 



bacteria, and seed-grains, require no food ; for, as has been seen, 1 

 no metabolism can be found in them even with the most 

 delicate means of investigation. Hence, when food is wanting in 

 their environment, they do not die. Here the clock has merely 

 stopped, it has not run down. 



In order, finally, to obtain an idea of the far-reaching adapta- 

 tions of individual organisms to special vital conditions of a very 

 unusual kind, so far as they have to do with food, it is necessary 



only to glance at the peculiar vital 

 relations of certain forms of Bacteria, 

 which have become known recently, 

 especially through the striking work 

 of Winogradsky ('88). 



The sulphur-bacteria (Beggiatoa) 

 constitute a family of microbes that 

 live in decaying pools and puddles 

 of both fresh and salt water. These 

 remarkable beings, which swarm about 

 in the water in the form of short rods 

 or long threads (Fig. 126), can exist 

 only when considerable quantities of 

 sulphuretted hydrogen are available. 

 Their metabolism requires this gas, 

 since they manufacture from it, by 

 oxidation, free sulphur, which they 

 store up in their tiny cell-bodies in 

 the form of fine, strongly refracting 

 granules (Fig. 126) ; by continued 

 oxidation they transform the sulphur 

 further into sulphuric acid, and in this 

 form excrete it to the outside. If the 

 sulphur-bacteria be brought into 

 spring- water that contains no sul- 

 phuretted hydrogen, they perish after 

 they have oxidised and excreted the 

 sulphur present in their bodies. 



Sulphuretted hydrogen, a gas that is poisonous to most organisms, 

 belongs, therefore, among their essential conditions of life. Without 

 it they cannot continue to exist. 



Winogradsky ('88) has pointed out a similar special adapta- 

 tion to peculiar vital conditions in the iron-bacteria. Bog iron- 

 ore moors are very generally known, occurring wide-spread in 

 marshy regions, with an oily, iridescent scum upon the surface of 

 their water and thick, reddish-yellow mud below. These are the 

 abode of the iron-bacteria, and the production of bog-ore is in 



1 Of. p. 132. 



FIG. 126. Various forms of sulphur- 

 bacteria. The granules in the interior 

 are particles of sulphur. (After 



are parces o sup 

 Schenk and Warming.) 





