n LIVING MATTEE 61 



succinic acid, and of various ethers, which eventually inhibit 

 fermentation and bring it to a standstill. The quantity of yeast 

 which is then deposited at the bottom of the vessel is conspicuously 

 augmented, showing that the cells of the Saccharomyces have- 

 abundantly reproduced themselves; but the organic nutritive 

 matters contained in the grape juice would, if they had not been 

 decomposed by the fermentative process, have sufficed for the 

 nutrition and multiplication of an incomparably larger amount of 

 yeast. 



Many pathogenic or non-pathogenic bacteria are able to dis- 

 solve gelatin or coagulated albumin for their nutrition and multi- 

 plication, and effect a putrid decomposition of the various culture 

 fluids or media, with development of carbonic acid, sulphuretted 

 hydrogen, ammonium sulphate, ammonia, and a simultaneous forma- 

 tion of new substances which generally have a toxic action, and are 

 the cause of virulent disease. 



In general those plants that contain no chlorophyll, and require 

 for their nutriment the organic matters already formed by other 

 plants or animals, utilise these substances merely as the raw 

 material of nutrition, submitting them further to special chemical 

 transformations. Fungi and bacteria, indeed, can adapt previously 

 inadequate substances to their nutrition. By means of invertase 

 they transform saccharose into glucose, by diastase starch is turned 

 into sugar, with the trypsin and pepsin ferments albumin is con- 

 verted into albumoses and peptone. Fungi have been proved to- 

 nourish in very different culture media, and are capable, with the 

 help of the organic compounds of carbon, and nitrogenous mineral 

 salts, of building up synthetically all the highly complex products 

 essential to the formation of protoplasm. They represent, accord- 

 ingly, in their metabolism an intermediate group between the 

 chlorophyll-containing plants and animals. 



The anabolic capacity of all animals, without exception, is 

 limited to the elaboration of the three principal groups of organic 

 substances, and their conversion into living protoplasm, with the 

 further synthetic formation of new substances which do not exist 

 in the plant world. They are incapable of reducing fully oxidised 

 organic substances so as to produce carbohydrates, fats, and 

 proteins; but they have the power (as we shall be able to- 

 demonstrate fully) of transforming carbohydrates into fats, albu- 

 moses and peptones into true proteins. 



Within the animal kingdom again we can distinguish different 

 groups, according to their nutritive requirements and correspond- 

 ing metabolism. Herbivores and frugivores more particularly 

 need to supplement the proteins with the carbohydrates in which 

 vegetable food is superabundant ; insectivores and carnivores, on the 

 contrary, profit by the many fats which abound in animal food. 

 Neither fats nor carbohydrates, however, are absolutely indis- 



