NOTES AND MEMORANDA. 231 



fested only by such compounds. Very much light is thrown 

 on this question by the study of the spectra and other 

 optical characters of coloured substances. These clearly 

 prove that when dissolved in any liquid the optical proper- 

 ties 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 particles are molecular 

 compounds with water, and not molecules of free dry 

 albuminous substances. 



Unfortunately, nothing definite is known respecting this 

 question, and all that can now be done by way of illustration 

 is to make some sort of a probable supposition. Taking 

 everything into consideration, 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 sup- 

 position the number of molecules in -roVo" of an inch cube 

 would be about 



Albumeu .... 17,000,000,000,000 



Water in molecular combiaation . 923,000,000,000,000 



940,000,000,000,000 



Since, however, the form of minute living organisms more 



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



convenient to give the numbers in a sphere of t oVo of ^.n 



inch in diameter. For this there would be about as follows : 



Albumen .... 10,000,000,000,000 

 Water in molecular combination . 490,000,000,000,000 



500,000,000,000,000 

 In the present state of our knowledge it is perhaps im- 

 possible 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 



