1878.] 



the Influence of Light upon Protoplasm. 



207 



withdrawal of air) failed entirely to produce any effect on such 

 organisms as were able to appear.* 



Experiments in which nitrogen was admitted into the exhausted 

 tubes before they were sealed gave similar results. 



The obvious inference that the presence of oxygen is essential to this 

 action of light is confirmed by the following experiment — many times 

 repeated — showing that the effect is in direct relation to the proportion 

 of free oxygen : — 



A Pasteur solution of half the strength given in our former paper, 

 and therefore, for reasons stated in that paper, difficult to sterilise by 

 insolation, was divided between six tubes. 



Two of these were simply sealed, and therefore contained an atmo- 

 sphere of ordinary air. 



Two were exhausted at the Sprengel pump till the gauge stood at a 

 height of 22 inches, when, by means of the apparatus described in the 

 Appendix, nitrogen was admitted, and the tubes being sealed, conse- 

 quently only contained about one-twentieth of oxygen in their atmo- 

 spheres. The remaining two tubes were exhausted thoroughly and 

 pure oxygen admitted in the same manner as the nitrogen. 



One tube of each series was incased in laminated lead, the com- 

 panion tube being insolated. 



In two days all the incased tubes were equally turbid with Bacteria. 



In two days more the insolated tube, with ^th. oxygen atmosphere, 

 was turbid with Torula and Bacteria. 



Next day after this, the insolated tube, with an atmosphere of 

 ordinary air, became hazy with Bacteria. 



The tube, with an atmosphere of pure oxygen, remained unchanged 

 for some days later, when a deposit of Torula commenced to form at 

 the bottom. 



We conclude, therefore, both from analogy and from direct experi- 

 ment, that the observed action on these organisms is not dependent on 

 light per se, but that the presence of free oxygen is necessary; light 

 and oxygen together accomplishing what neither can do alone : and 

 the inference seems irresistible that the effect produced is a gradual 

 oxidation of the constituent protoplasm of these organisms, and that, 

 in this respect, protoplasm, although living, is not exempt from laws 

 which appear to govern the relations of light and oxygen to forms of 

 matter less highly endowed. f A force, which is indirectly absolutely 



* The commonest form of organism in these exhausted tubes consisted of filaments 

 of varying length, ranging perhaps from -g-^o" to 3^0", often curvilinear, composed 

 of minute spherules in linear series, with motion usually vibratory and undulating, 

 frequently progressive. 



f That the amount of free oxygen present need not be large to produce a definite 

 action upon Bacteria is shown by the fact that tubes containing Pasteur solution 

 with a supernatant layer of vaseline, excluding all air, except that previously dissolved 

 in the solution, if encased, in a few days become turbid, but may be kept clear for 



