220 Dynamic Theory. 



are due. We shall hear-a good deal more of it. The substances extracted from the sol- 

 uble debris of the yeast are similar to those obtained from animal tissues. 



Yeast subjected to the process mentioned above is really digested by its ferment. 

 Similar action resulting in similar products is obtained by placing warm, diluted sul- 

 phuric acid, or such alkalies as potash and barytes, in contact with proteids, gluten, al- 

 bumen, &c., under certain conditions; a fact which, to my mind, proves the ultimate 

 identity between, or, at least, common parentage of, cbemical and vital processes. 



Yeast, like other organic bodies, is subject to the effects of poisons, some of which act 

 by coagulating the albumen and thus disorganizing the tissues. Among these are nitrate 

 of silver, chlorine, iodine, soluble iron, tannin, creosote, chloroform, alcohol when 

 above 20 per cent., &c. Yeast is always acid, and if the acidity be neutralized by lime 

 water it will soon reappear. 



The action of the fungus mucors in a fermentable solution is similar 

 to that of the saccharomyces family. They grow at the expense of the 

 infusion and promote alcoholic fermentation, though not with the same 

 facility. The mucor racemosus produces 100 parts of alcohol to 123. 1 

 of carbonic acid, while the ordinary yeast produces 100 parts alcohol 

 to 96.3 carbon dioxide, which shows the mucor to be a more vigorous 

 eater of carbon ( sugar ) for the work it does. 



When growing on horse manure the mucor produces, from a spread- 

 ing mycelium, numerous strong filaments the thickness of a hair, on 

 the top of each of which a little round head is developed, which be- 

 comes the bearer of spores. But if these spores are sown in a ferment- 

 able solution their mode of life undergoes a radical change. ' ' Either 

 short germinating utricles shoot forth, which soon form themselves into 

 rows of gemules, or the spores swell to large round bladders filled 

 with protoplasm and shoot forth on various parts of their surface in- 

 numerable protuberances which, fixing themselves with a narrow basis, 

 soon become round vesiculate cells, and on which the same kind of 

 sprouts which caused their production are repeated formations which 

 remind us of the fungus of fermentation called globular yeast. " ( Cooke. ) 

 A number of fungoid aud parasitic organisms will live in a fermentable 

 fluid in which, however, . they do not set up alcoholic fermentation, 

 which shows, I think, that they are not associated with a zymase, or 

 ferment of the right genus. 



To sum up, in relation to yeast, its congeners and imitators : They 

 are complete organisms having everything within themselves necessary 

 to lead a parasitic existence, like an animal or vegetable parasitic cell. 

 They are accompanied, in some if not all cases, by an accessory fer- 

 ment, zymase, which assists them in the digestion of insoluble food. 

 They respire by the absorption, from the solution in which they live, of 

 oxygen, which they exhale with the carbon of their own tissues, form- 

 ing carbonic dioxide, C 2 . Yeast sets up alcoholic fermentation in a 

 solution of pure sugar in the absence of all trace of ( free ) oxygen, but 

 without developing ; that is, the yeast, or its zymase, does the work of 

 splitting the sugar without growing itself. 



