PROBLEMS OF PHYSIOLOGICAL CHEMISTRY. 513 



ner we are to proceed in order to arrive at the object to be accom- 

 plished. 



For a series of the most important disclosures, we are indebted to 

 those investigations which have been devoted to the life-processes of 

 the lowest organisms, consisting of single cells. Not that we have 

 here progressed any further than elsewhere, but we have attained the 

 certainty that the most important processes take place in the cells 

 themselves, and that substances are formed which are able to produce 

 powerful chemical changes. The processes to be first considered are 

 those included under the general name of fermentation. 



The first known process of fermentation is that which cane-sugar 

 undergoes. A fungus, the so-called yeast, converts the sugar into 

 glucose, and then decomposes this into alcohol and carbonic acid, with 

 the simultaneous formation of small quantities of other products, such 

 as succinic acid, glycerine, etc. The amount of yeast is not increased 

 unless other substances, particularly nitrogenous organic and certain 

 inorganic salts required in building up the body of the cells, are pres- 

 ent. From this it appears that various chemical processes take place 

 within the cell, the most striking of which is the decomposition of the 

 sugar. How this takes place is a question which has been largely 

 discussed. From the circumstance that carbonic acid and alcohol are 

 produced in such proportions that the quantities of carbon, hydrogen, 

 and oxygen contained in them are just sufficient to form the sugar, 

 one might suppose that the decomposition is very simple ; but, not- 

 withstanding all attempts, the same reaction has never been produced 

 without the aid of yeast. Two hypotheses have been proposed to ex- 

 plain this phenomenon : the one assumes that the yeast-cell contains a 

 ferment which splits the glucose directly into carbonic acid and al- 

 cohol, the same as invertin changes cane-sugar into dextrose and 

 lsevulose ; the other, on the contrary, considers the decomposition of 

 the grape-sugar as an effect of the vital action of the yeast-cells, com- 

 parable to the conversion of albumen into carbonic acid, water, and 

 urea in the organism of mammals. 



In order to form an opinion of the value of these hypotheses, we 

 will briefly indicate the points of view whence they have been pro- 

 jected. In the first theory consideration is given chiefly to the simi- 

 larity which the outward appearance of the yeast fermentation has 

 with certain chemical processes, such as the decomposition of sugar by 

 invertin. In both cases the presence of a small amount of yeast or in- 

 vertin suffices to decompose a comparatively large quantity of sugar, 

 without any apparent change being produced in the yeast or in the 

 invertin. This has given rise to the supposition of the existence of 

 an alcohol ferment in the yeast ; a theory which will be verified, when 

 the suspected ferment shall be separated from the yeast, as has already 

 been done with the invertin. All experiments, however, which have 

 been made in this direction have resulted negatively, and hence the 

 vol. xx. 33 



