CONTRIBUTIONS TO SCIENCE. 



It forbids the physiologist from imagining that structural 

 details of infinitely small dimensions can furnish an explanation 

 of the infinite variety which exists in the properties and functions 

 of the most minute organisms. 



A microscopic germ is, we know, capable of development 

 into a highly organised animal. Another germ, equally micro- 

 scopic, becomes when developed an animal of a totally different 

 kind. Do all the differences, infinite in number, which distin- 

 guish one animal from another arise each from some difference 

 in the structure of the respective germs ? Even if we admit 

 this as possible we shall be called upon by the advocates of 

 Pangenesis to admit still greater marvels. For the microscopic 

 germ, according to this theory, is no mere individual, but a 

 representative body, containing members collected from every 

 rank of the long-drawn ramification of the ancestral tree, the 

 number of these members being amply sufficient not only to 

 furnish the hereditary characteristics of every organ of the body, 

 and every habit of the animal from birth to death, but also to 

 afford a stock of latent gemmules to be passed on in an inactive 

 state from germ to germ, till at last the ancestral peculiarity 

 which it represents is revived in some remote descendant. 



Some of the exponents of this theory of heredity have 

 attempted to elude the difficulty of placing a whole world of 

 wonders within a body so small and so devoid of visible structure 

 as a germ, by using the phrase structureless germs. Now, one 

 material system can differ from another only in the configuration 

 and motion which it has at a given instant. To explain differ- 

 ences of function and development of a germ without assuming 

 differences of structure is therefore to admit that the properties 

 of a germ are not those of a purely material system. 



A paper " On Stresses in Earified Gases arising from 

 Inequalities of Temperature," by Professor Maxwell, was 

 read before the Eoyal Society on April 11, 1878, and 

 published in the Phil. Trans, for 1879. The notes and 

 appendix added to the paper in May and June 1879 em- 

 bodied the results of Maxwell's last investigations in the 

 kinetics of gases. In this paper Maxwell showed that when 

 inequalities of temperature exist in a gas the pressure at a 

 point is not generally the same in all directions, but the 

 maximum and minimum pressures differ by an amount depend- 

 ing on the rate of change of the increase of temperature per 

 unit length in the direction in which this rate is greatest 



