366 GENERAL PHYSIOLOGY 



therefore, a corresponding increase of both the assimilatory and 

 the dissimilatory phases of the metabolism of the tissue-cells. 



A similar condition exists among plants. The carbonic acid of 

 the air serves the plant as food and is split up in the chlorophyll- 

 bodies of the living cells. The carbon set free is then employed, 

 together with the water received through the roots, for the 

 synthesis of starch, or assimilation. If more carbonic acid be 

 brought to the plant than is contained in the air as its necessary 

 vital condition, the splitting-up of carbonic acid and the assimila- 

 tion of starch are increased in equal measure up to a certain 

 degree. The increase of the quantity of food, therefore, conditions 

 also an increase of metabolism. 



But this does not always hold good. Regarding oxygen, we 

 know, at least, that its increase in quantity beyond the amount 

 necessary for life is essentially without influence upon the 

 metabolism of the tissue-cells. The tissue-cells of the human 

 body are within wide limits independent of the percentage and 

 the partial pressure of oxygen in the air, and experience no 

 augmentation of metabolism with increase of the income of 

 oxygen. Whether the same is true of free-living cells and the 

 cells of lower animals still needs investigation. 



In many cases the increased income of food that is accompanied by 

 an increase of metabolism causes also a clearly recognisable increase 

 in change of form. While in the tissue-cells of the human body, 

 as has been seen, the food that is introduced beyond the necessary 

 quantity is under normal conditions destroyed excepting an ex- 

 tremely small fraction, and is not employed for the increase of 

 living substance, in many unicellular organisms, especially in 

 Bacteria and Infusoria, an increase of the assimilatory processes, 

 and in unequal measure of the dissimilatory processes also, takes 

 place with increase of food. The result of this is an increase of 

 living substance, a " fattening," which is expressed in rapid growth 

 and continued cell-division. If, e.g., putrefactive bacteria {Bac- 

 terium termo, Spirillum undada, etc.) be transferred from a liquid 

 in which they are living in small numbers, into a good nutrient 

 solution, such as an infusion of hay, they at once begin to increase 

 enormously, until from the few bacteria with which the nutrient 

 solution was infected many millions may have developed. If there 

 be placed in such a hay-infusion swarming with putrefactive 

 bacteria a Paramcccium, which nourishes itself upon such bacteria, 

 in a few days it may be seen that from this one infusorian 

 thousands have been produced, so that they give to the liquid a 

 milky cloudiness. Thus the assimilatory phase of the metabolism 

 of these micro-organisms becomes enormously increased by 

 superfluity of food. 



Under pathological conditions also similar phenomena occur 

 in the tissue-colls of the human body, and modern pathology 



