1878.] On the Influence of Light upon Protoplasm. 199 

 by Sir W. Thomson's statical theory, in the proportion of 1 + 



150(r+g) 



to unity, where v is the speed of the tide, and r is the quantity defined 



in Thomson and Tait's Nat. Phil., § 840 (28), viz., 19 x the coeffi- 



bwa? 



cient of rigidity. 



The last part of the paper contains a discussion of results, and a 

 non-mathematical summary of what precedes. 



IV. " On the Influence of Light upon Protoplasm." By Arthur 

 Downes, M.D., and Thomas P. Blunt, M.A. Oxon. Com- 

 municated by J. Marshall, F.R.S., Surgeon to University 

 College Hospital. Received October 9, 1878. 



This paper is in continuation of, and supplementary to, a previous 

 communication* in which we recorded the first part of an investiga- 

 tion on the effect of light upon Bacteria and other organisms associated 

 with putrefaction and decay. The chief conclusions to which those 

 observations led us were briefly as follow : — 



(I.) Light is inimical to, and under favourable conditions may 

 wholly prevent, the development of these organisms; its action on 

 Bacteria being more energetic than upon the mycelial (and torulaceous) 

 fungi which are prone to appear in cultivation-fluids. 



(2.) The fitness of the cultivation-fluid as a nidus is not impaired by 

 insolation. 



We found also that tubes, containing a cultivation-fluid and plugged 

 with cotton-wool, when removed to a dark place after exposure to the 

 sun for a sufficient period, remained perfectly clear and free from 

 organisms for months, and we naturally thought that the contents had 

 been reduced to permanent sterility. The following facts, however, 

 compel us to suspend for the present our conclusions on this point. 

 Of the many tubes which we insolated last year we finally kept only 

 three. Two of these — containing Pasteur solution of the composition 

 given in our former paper — had been exposed to sunlight for three 

 weeks in June, 1877; the third tube contained urine and had been 

 insolated for about two months — commencing July 26th. In each 

 case corresponding tubes which were covered with laminated lead, so 

 as to exclude light, had swarmed with Bacteria in the course of two or 

 three days, but the three tubes of which we speak not only were perfectly 

 pellucid at the time they were removed from the light but, although 

 kept in a warm room, remained clear all through the winter. On 

 February 25th, 1878, however, — eight months after we had placed 



* "Proc. Roy. Soc," vol. xxvi, p. 488. 



P 2 



