YEAST. 583 



and " cell-wall" are essential to a cell ; the other, that cells are usually 

 formed independently of other cells; but, in 1839, it was a vast and 

 clear gain to arrive at the conception that the vital functions of all the 

 higher animals and plants are the resultant of the forces inherent in the 

 innumerable minute cells of which they are composed, and that each of 

 them is, itself, an equivalent of one of the lowest and simplest of 

 independent living beings the Torula. 



From purely morphological investigations, Turpin and Schwann, 

 as we have seen, arrived at the notion of the fundamental unity of 

 structure of living beings. And, before long, the researches of the 

 chemists gradually led up to the conception of the fundamental unity 

 of their composition. 



So far back as 1803, Thenard pointed out, in most distinct terms, 

 the important fact that yeast contains a nitrogenous " animal " sub- 

 stance ; and that such substance is contained in all ferments. Before 

 him, Fabroni and Fourcroy speak of the " vegeto-animal " matter of 

 yeast. In 1844, Mulder endeavored to demonstrate that a peculiar 

 substance, which he called " proteine," was essentially characteristic 

 of living matter. 



In 1846, Payen writes: 



I recognize, in the numerous facts which have come under my observation, 

 a law which has no exception, and which will lead us to regard vegetal life 

 under a new aspect. If I am not mistaken, whatever we can discern under the 

 form of cellules and vessels represents nothing but protective envelopes, reser- 

 voirs, and conduits, wherein the animated bodies which secrete and construct 

 them find a home, food, and the means of transporting it, and where they 

 throw off and reject excretory matter. 



And awain : 



To state fully the general fact, I repeat that bodies which discharge the func- 

 tions performed by the tissues of plants, are formed of elements which, in slightly 

 different proportion, make up animal organisms. Hence we are led to recognize 

 a wonderful unity of elementary composition in all living bodies. 1 



In the year (1846) in which these remarkable passages were pub- 

 lished, the eminent German botanist, Yon Mohl, invented the word 

 " protoplasm," as a name for one portion of those nitrogenous contents 

 of the cells of living plants, the close chemical resemblance of which to 

 the essential 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 investigators, among 

 whom Cohn, Max Schulze, and Kuhe, must be named as leaders, have 

 accumulated evidence, morphological, physiological, and chemical, in 

 favor of that " wonderful unity of elementary composition in all living 

 bodies," into which Payen had, so early, a clear insight. 



1 " Mem. sur les Developpements des Yegetaux," etc. " Mem. Presentees," ix., 

 1846. 



