132 YEAST iv 



close chemical resemblance of which to the essen- 

 tial constituents of living animals is so strongly 

 indicated by Payen. And through the twenty- 

 five years that have passed, since the matter of 

 life was first called protoplasm, a host of investi- 

 gators, among whom Cohn, Max Schulze, and 

 Klihne must be named as leaders, have accum- 

 ulated evidence, morphological, physiological, and 

 chemical, in favour of that " immense unite de 

 composition elementaire dans tous les corps vivants 

 de la nature," into which Payen had, so early, a 

 clear insight. 



As far back as 1850, Cohn wrote, apparently 

 without any knowledge of what Payen had said 

 before him : 



" The protoplasm of the botanist, and the contractile sub- 

 stance and sarcode of the zoologist, must be, if not identical, yet 

 in a high degree analogous substances. Hence, fvom this point 

 of view, the difference between animals and plants consists in 

 this ; that, in the latter, the contractile substance, as a primordial 

 utricle, is enclosed within an inert cellulose membrane, which 

 permits it only to exhibit an internal motion, expressed by the 

 phenomena of rotation and circulation, while, in the former, it 

 is not so enclosed. The protoplasm in the form of the primordial 

 utricle is, as it were, the animal element in the plant, but 

 which is imprisoned, and only becomes free in the animal ; or, 

 to strip off the metaphor which obscures simple thought, the 

 energy of organic vitality which is manifested in movement is 

 especially exhibited by a nitrogenous contractile substance, 

 which in plants is limited and fettered by an inert membrane, 

 in animals not so." 1 



1 Cohn, " Ueber Protococcus pluvialis, " m the Nova Acta for 

 1350. 



