286 GENERAL PHYSIOLOGY 



and the small accumulations of protoplasm break up, their sub- 

 stance flowing partly centrifugally, partly centripetally. In this 

 manner the pseudopodia again become smooth, their streaming 

 becomes more active, and after a half-hour the same appearance 

 is present as at the beginning of the experiment. 



Engelman was able also to determine that ciliated cells are 

 capable of maintaining life for several hours without oxygen. 

 Hermann ('67-'68) has shown the same for muscle by placing one of 

 two exactly similar gastrocnemius muscles of the frog in a 

 cylinder containing pure hydrogen, the other in a cylinder filled 

 v/ith air containing oxygen, and testing their irritability by means 

 of electric stimuli, which both muscles received at the same time. 

 The muscle in pure hydrogen lived several hours before becoming 

 inexcitable, while the muscle in oxygen continued to live 

 unchanged. From all these experiments it follows that certain 

 cells and tissues can maintain life for a considerable time in a 

 medium free of oxygen. 



This fact, especially in regard to muscle, has been variously 

 employed as the basis of an unjustified conclusion. Since 

 Hermann has shown that no free oxygen can be extracted 

 by means of the gas-pump from an excised bloodless muscle, the 

 inference has been drawn that muscle, while able to perform 

 movements for a long time without external oxygen, works solely 

 by means of cleavage-processes. This conclusion is unjustified, 

 since, from the fact that no free oxygen can be pumped out of a 

 muscle, it ought not to be inferred that no oxygen whatever 

 capable of being used for oxidation is longer present in the 

 muscle. On the contrary, it is very probable that in the muscle, 

 perhaps in the sarcoplasm, there exists in combination oxygen that 

 during activity is continually being consumed by the contractile 

 particles for their oxidisation. As a matter of fact, hsemoglobin 

 has been found in the muscles of some invertebrates that 

 possess in their blood no haemoglobin whatever. It must hence 

 be supposed that in cells that continue to live for a long time 

 in the absence of oxygen, oxidation-processes still take place, 

 certain complexes of atoms of the living substance withdrawing 

 the oxygen for their own oxidation from others that contain 

 it in loose combination, until finally all the oxjgeii is con- 

 sumed and combined into the cleavage-products. However this 

 may be, in the absence of oxygen all living organisms perish after 

 a shorter or longer time. Without oxygen no life can exist 

 permanently. 



There are some apparent exceptions to this principle ; there 

 are organisms that apparently can continue to live without 

 (jxygen. 



At first sight the green plants appear to form such an exception, 

 and at one time they were really believed to do so.' In one respect 



