The President's Address. By H. C. Sorhy, F.B.S., &c. 117 



ignored in many large and important chemical works, and yet pro- 

 bably many of the phenomena of life are manifested only by such 

 compounds. Yery much light is thrown on this question by the 

 study of the spectra and other optical characters of coloured sub- 

 stances. These clearly prove that when dissolved in any liquid the 

 optical properties of the solution depend in part on the nature of 

 the solvent, and are by no means the same as they would be if 

 minute particles of the solid substance were diffused in the liquid. 

 These facts cannot, I think, be explained unless we conclude that 

 the solvent is to some extent in the state of molecular combination 

 with the substance dissolved. This molecular affinity is also in 

 some cases manifested by a swelling up of a solid substance when 

 placed in some liquids, even when perfect solution occurs to a very 

 limited extent. Such a condition appears to be very characteristic 

 of the living tissues of animals, and makes it sufficiently probable 

 that the ultimate living jDarticles are molecular compounds with 

 water, and not molecules of free dry albuminous substances. 



Unfortunately, nothing definite is known respecting this ques- 

 tion, and all that can now be done by way of illustration is to make 

 some sort of a probable supposition. Taking everything into con- 

 sideration, it appears to me that, as a reasonable example, we may 

 assume that living albuminous tissue contains one-half of its volume 

 of water mechanically mixed, and one-fourth its volume of free 

 albumen united molecularly with an 'equal volume of water. On 

 this supposition the number of molecules in roVa of an inch cube 

 would be about 



Albumen 18,000,000,000,000 



Water in molecular combination . . . . 992,000,000,000,000 



1,010,000,000,000,QOO 



Since, however, the form of minute living organisms more 

 nearly approximates to spheres than to cubes, it will be more con- 

 venient to give the numbers in a sphere of roV^ of an inch in 

 diameter. For this there would be about as follows : 



Albumen 10,000,000,000,000 



Water in molecular combination .. .. 520,000,000,000,000 



530,000,000,000,000 



In the present state of our knowledge it is perhaps impossible 

 to say whether or not the essential characters of living particles are 

 due to the structural arrangement of the molecules of this combined 

 water as well as of those of the albumen, and whether or not in 

 considering the possible variations in structure the total number of 

 molecules should be taken into account. The very small relative 

 amount of dry matter in some living animals does, however, make 



