302 THE ANIMAL CELL. 



red corpuscles at one period of their existence, viz., in their juve- 

 nile form, are nucleated, and that under certain conditions, as after 

 copious hemorrhages, such nucleated corpuscles may occur in the 

 circulating blood in large numbers. In the bone-marrow, where 

 they are apparently formed, they are always present. 



As all manifestations of life are intimately associated with 

 chemical changes which bring about a transformation of potential 

 into kinetic energy, such changes must of necessity occur in every 

 living cell. These changes, moreover, must vary with the func- 

 tion which the cell is to perform, and will hence differ, to a 

 certain extent at least, with the different tissues of the complex 

 organism. In the monocellular organisms, where all the various 

 functions are performed by the single cell, all these varying changes 

 must hence be represented. But it is to be inferred that in accord- 

 ance with the greater simplicity in structure the chemical changes 

 also must be of a simpler character. We should hence expect that a 

 study of the chemical processes which take place in such low forms 

 of life would furnish us with a better insight into the metabolism 

 of the complex organism than could be attained from an investiga- 

 tion of the higher forms. Unfortunately, however, this is almost 

 an impossibility with the usual chemical and physical methods, for 

 in attempting such a study we are met with a most serious obstacle, 

 viz., our inability to maintain the life of the individual cell during 

 such an investigation. We would consequently have no proof that 

 those products which we could isolate from the dead cells were 

 present as such in the living organism. The technical difficulties, 

 moreover, which stand in the way of such a study are almost insur- 

 mountable. With microchemical methods, it is true, something 

 more definite might be accomplished, and although this branch of 

 investigation is still in its infancy, it has already furnished us with 

 a certain amount of valuable information. The great advances 

 which have thus been made in our knowledge of the structure 

 of cells have largely been accomplished in this manner. Upon 

 the chemical processes themselves, however, which take place 

 in the cell, not much light has as yet been thrown in this 

 manner. We are consequently dependent for our knowledge of 

 the metabolic processes which take place in the living body upon 

 a study of the individual tissues as such, and the changes which 

 result in certain substances when introduced from without. An 

 analysis of these tells us in what form the various food-stuffs are 

 represented in the individual cells. By then studying the vari- 

 ous decomposition-products which can be isolated from the tissues, 

 we can in a measure form an idea of the manner in which these 

 products were produced and of the form in which they were 

 represented in the original and more complex molecule. With 

 some tissues, however, this is more difficult than with others. The 

 most satisfactory results, on the whole, regarding the chemical 

 structure of the individual cell have thus far been obtained from 



