233 NOTES AND MEMORANDA. 



be taken into account. The very small relative amount of 

 dry matter in some living animals does, however, make it 

 very probable that molecularly combined water really plays a 

 part in their structure ; and on the whole we may, I think, 

 base our provisional calculations on the total number of 

 molecules given abpve. 



The Theory of Invisible Germs. 



The relation between the size of the smallest object that 

 can be seen, and that of the ultimate molecules of living 

 matter, is manifestly a question of great importance in con- 

 nection with the theory of germs. If the ultimate mole- 

 cules were much larger than they appear to be, there would 

 be serious objections to the theory ; but, as far as we can 

 judge, they are sufficiently small to make it possible for an 

 almost endless variety of germs to exist, each having a dis- 

 tinct structural character, and yet each so small that there is 

 no probability of our ever being able to see them, even as 

 indefinite points. Thus, according to the principles de- 

 scribed above, a sphere of organized matter one-tenth of the 

 diameter of the smallest particle that could be clearly de- 

 fined with our highest powers, might contain a million 

 molecules of albumen and moleculary combined water. 

 Variations in number, chemical character, and arrangement, 

 would in such a case admit of an almost boundless variety 

 of structural characters. The final velocity with which such 

 extremely minute particles would subside in air must be so 

 slow that they could penetrate into almost every place to 

 which the atmosphere has access. 



Darwiri's Theory of Pangenesis. 



Darwin's theory of pangenesis is an attempt to give some- 

 thing like a reasonable explanation of the phenomena of 

 inheritance, and is not necessarily connected with the ques- 

 tion of the evolution of new species. A full account of the 

 theory will be found in his work on the variation of animals. 

 At p. 374 of vol. ii. he says that " he assumes that cells before 

 their conversion into completely passive or formed material, 

 throw ofi" minute granules or atoms, which circulate freely 

 throughout the system, and when supplied with proper nutri- 

 ment multiply by self-division, subsequently becoming de- 

 veloped into cells like those from which they were derived. 

 These granules for the sake of distinctness may be called 

 cell-gemmules, or, as the cellular theory is not fully estab- 

 lished, simply gemmules. They are supposed to be trans- 

 mitted from the parents to their offspring, and are generally 



