THE GENERAL CONDITIONS OF LIFE 



283 



interest here. It is, however, interesting to glance at the results 

 of complete removal of oxygen. 



The final results of complete removal of oxygen are evident. 

 If oxygen be a general condition of life, all living substance must 

 perish after its complete withdrawal. This has been shown by 

 experiments that have been performed partly upon single cells, 

 partly upon tissues, and partly upon multicellular organisms. But 

 different kinds of cells perish after different intervals of time, 

 some very rapidly, some gradually, just as do different organisms 

 upon withdrawal of food. The cells of the nervous system are 



FIG. 129. /. Engelmann's gas-chamber. An annular space is closed below by a glass plate and 

 above by a metal cover, the latter having in its middle a cover-glass for the examination of a 

 hanging drop ; a,a', are tubes that open into the cavity of the ring and serve to heat the latter 

 by conveying through it warm water ; b,b' are tubes that open into the glass-covered chamber 

 and serve for the passage of the gas ; the drop hanging upon the cover-glass with its living 

 contents is bathed by the gas in the chamber. II. Arrangement of the experiment for in- 

 vestigation in pure hydrogen, a, Kipp's apparatus for the preparation of hydrogen ; b, two 

 wash-bottles for purifying the hydrogen ; c, microscope, upon which is the gas-chamber con- 

 taining the hanging drop. 



the most sensitive to absence of oxygen. Hence without oxygen 

 the higher vertebrates, in which the movements of respiration, the 

 activity of the heart, etc., are dependent upon the cells of the 

 nerve-centres, perish very soon with violent phenomena of stimu- 

 lation. Other kinds of cells, however, continue to live for a 

 considerable time even in a medium wholly free from oxygen. 



By the use of hydrogen, a gas absolutely indifferent to the 

 organism, oxygen may be readily and completely excluded with- 

 out introducing into the experiment other harmful factors. Since 

 in a closed space atmospheric air, in which oxygen is the sole 



