March O-*, 1895.] 



SCIENCE. 



311 



this view is the established fact that the gas 

 conducts itself as if made up of individual 

 particles, while any allotropic form of nitro- 

 gen, which is heavier than this, must, ac- 

 cording to all that we know of such mat- 

 ters, consist of more complex molecules 

 than nitrogen itself. 



Ira Remsen. 

 Johns Hopkixs University. 



THE FUNDAMENTAL DIFFEREXCE BE- 

 TWEEN PLANTS AND ANIJfALS* 



To the advanced student, as to the inves- 

 tigator, the question of a definite and ac- 

 curate distinction by which all ti'ue plants 

 can be distinguished from all true animals, 

 is a question of minor interest. To the be- 

 ginning student the question, on the con- 

 trarj', is a pressing one for which the an- 

 swer is urgentl}' claimed. Thus I am led 

 to believe that the definition given below, 

 though it cannot add anj-thing essential to 

 the conceptions of investigators, will never- 

 theless prove valuable to teachers of biologj'. 



The usual method of drawing a contrast 

 between the animal and vegetable king- 

 doms, for the purpose of establishing some 

 sort of definition of the two in students' 

 minds, is to leave out of consideration the 

 lower forms, and to take into consideration 

 only the higlier forms, on the one side plants 

 with chlorophyll, on the other the multicel- 

 lular animals or so-called Metazoa. It is 

 then easy to establish a difference in the 

 physiological nutritive processes, emphasiz- 

 ing the synthetic processes, particularly the 

 power of bringing free nitrogen into com- 

 binations on the i)art of plants and the ab- 

 sence of the synthetic process among ani- 

 mals. It is much to be regretted that this 

 method of defining animals and plants has 

 been and still is very widely used, for it 

 leads to inevitable perplexity, because the 

 next thing almost wliich the student must 



* Rea<l before the American Society of Morpholo- 

 gists at Baltimore, December, 1894. 



learn is that the distinction does not hold 

 true. On the one hand, he learns that 

 among plants there are manj- forms without 

 chlorophyll and that these cannot bring 

 nitrogen into combination and must secure 

 proteid food. On tlie other hand, he learns 

 that among animals numerous synthetic 

 processes occur, and if he takes up the 

 study of medical physiology he learns many 

 instances of synthetic chemical work on the 

 part of the mammalian body. Dr. F. Pfaft" 

 has kindlj- indicated to me two striking in- 

 stances of synthesis in the mammalian body, 

 first, the formation of glycuronic acid after 

 the administration of camphor or turpen- 

 tine, and second, the formation of hippuric 

 acid after the administration of benzoine. 



Another distinction often drawn between 

 animals and plants is that of the presence 

 or absence respectively of internal digestive 

 organs. But this again soon leaves the 

 student in the lurch, for the first amoebea 

 he examines knocks that distinction out of 

 the ring. 



We may, however, I think, rightly define 

 the two primaiy divisions of the living 

 world thus: 



Animals are organisms wliich take part 

 of their food in the form of concrete parti- 

 cles, which ai-e lodged in the cell proto- 

 plasm by the activity of the protoplasm 

 itself. 



Plants are organisms which obtain all 

 their food in either the liquid or gaseous 

 form bj' osmosis (diffusion). 



There are certain facts which appear to 

 invalidate these definitions. The most im- 

 portant of such facts, so far as known to 

 me, is atforded bj^ the Mj'xomycetes, which, 

 as well known, while in the Plasmodium 

 stage of their life-cj'de, take solid particles 

 of food very mucli after Amu'ba-fashion. 

 Through the kindness of Professors W. G. 

 Farlow and G. L. Goodale, I have learned 

 that there are no other plants which at the 

 present time are known to take solid food 



