MODERN CONCEPTION OF PROTOPLASM. 31 



the waste products which are formed as the ashes of 

 life. 



There are indeed some organs which we have not 

 mentioned, such as the spleen, which seems to be an area 

 for the multiplication of red blood corpuscles (fishes, 

 newts, embryo-mammals) or for the destruction of worn- 

 out corpuscles (mammals), and the thyroid gland, which 

 seems to have to do with keeping the blood at a certain 

 standard of efficiency ; but what we have said is perhaps 

 enough to convey a general idea of the processes of life 

 in a higher animal. 



In conclusion, it is perhaps useful to remark that when in the 

 course of further studies the student meets with organs which are called 

 by the same name as those found in man or in Mammals, as, for 

 example, the "liver" of the Molluscs, he must be careful not to 

 suppose that the function of such a " liver " is the same as in Mammals, 

 for comparatively little investigation into the physiology of the lower 

 types of animal life has as yet been made. At the same time, he must 

 clearly recognise that the great internal activities are in a general way 

 the same in all animals ; thus respiration, whether accomplished by 

 skin, or gills, or air-tubes, or lungs, by help of the red pigment (haemo- 

 globin) of the blood, or of some pigment which is not red, or occurring 

 without the presence of any blood at all, always means that oxygen is 

 absorbed almost like a kind of food by the tissues, and that the carbon 

 dioxide which results from the oxidation of part of the material of the 

 tissues is removed. 



MODERN CONCEPTION OF PROTOPLASM 



The activities of animals are ultimately due to physical 

 and chemical changes associated with the living matter or 

 protoplasm. This is a mere truism. We do not know 

 the nature of this living matter ; perhaps our most certain 

 knowledge of it is, that in our brains its activity is 

 associated with consciousness. 



When more is known in regard to the chemistry and 

 physics of living matter, it may be possible to bring vital 

 phenomena more into line with the changes which are 

 observed in inorganic things. At present, however, it is 

 idle to deny that vital phenomena are things apart. Not 

 even the simplest of them can be explained in terms of 

 chemistry and physics. Even the passage of digested food 

 from the gut to the blood vessels is more than ordinary 



