A. E. HILTON OX THE NATURE OE LIVING ORGANISMS. 49 



long periods of time, have sprung all the bewildering varieties of 

 the teeming life of our planet — the myriad forms which are now 

 extinct, as well as those which are .^tiil evolving, including man 

 himself. 



In closing with a few general considerations, we may remind 

 ourselves that the goal of experimental biology is still a long way 

 off. Life in its proper sense cannot yet be produced by artificial 

 means from dead matter, notwithstanding sensational announce- 

 ments which appear from time to time in newspapers. Further, 

 we have no exact definition of plasm; so that we cannot at 

 present formulat' a standard of parity. There are doubtless as 

 many atomic arrangements of plasm molecules as there are 

 vai ieti< s of organisms. Heredity is caused by chemical processes, 

 under similar conditions, repeating themselves: variations are 

 explainable by changes in molecular constitution, owing to ah. -ra- 

 tions in sex elements <>r changes in environment. The differ- 

 ence between plant ami animal plasm is evidently a deeply seated 

 molecular difference, not yet fathomed. In order of time, plants 

 must have appeared upon the earth before animals, because 

 animals can only manufacture plasm from materials organised 

 from inorganic matter by plants. The animal kingdom is there- 

 fore parasitic on the vegetable kingdom, and represents a higher 

 development. The highest developments are found in the 

 nervous and mental functions of the nobler animals, in which 

 plasm conspicuously plays its all-important part. 



In conclusion, any attempt to gain a forced clearness in 

 regard to plasm is, of course, only misleading. What is needed 

 is not speculation, but more facts. Therein lies work for the 

 future for all skilled investigators. Meanwhile, our question is, 

 " Can we combine the ideas before us into a practical working 

 notion of the ' automatic chemical machinery ' we have been 

 considering ? ' I think we can. Incomplete as our information 

 is, I believe that in the facts already ascertained we have 

 sufficient materials for a mental model of living matter, which 

 will work well enough to be exceedingly useful, and can be 

 improved as knowledge advances. The construction of such a 

 thought-model requires a mental effort ; but the effort is worth 



Journ. Q. M. C, Series II.— No. GO. -i 



