16 OF DIFFERENCE IN STRUCTURE. 



plasm, and then this latter is changed into the lifeless 

 nutrient materials which are taken up by the several 

 forms of bioplasm which are concerned in the forma- 

 tion of the tissues. But bioplasm exists at all ages. 

 It is to be detected in every tissue, be it healthy or 

 diseased, simple or complex. Without it the tissue 

 could not grow, and could not be repaired if it was 

 injured. Without this it could not be said to live. In 

 fact, the tissue that is formed is not living. The bio- 

 plasm only is alive, and the proportion of bioplasm 

 decreases as the tissue grows old. A_t first the little 

 speck of matter out of which the man or animal or 

 plant is to be formed consists entirely of bioplasm, 

 then soft temporary tissue appears, but the propor- 

 tion of bioplasm to tissue remains very considerable 

 for some time. Gradually, however, the tissue in- 

 creases, and the proportion of living matter decreases, 

 at last becoming so small that in many textures it does 

 not amount to the T^th part of the whole. In many 

 cases this small particle of living matter dies, and 

 then the tissue is incapable of further change. It is 

 all dead. If injured it cannot be repaired. It is no 

 longer nourished. It no longer performs its function. 

 It may yet remain connected with the living body, but 

 it is as dead as the lifeless dried up leaf that still clings 

 to the living stem, though every vital connection has 

 long since been severed. 



29. Of difference in structure. On taking a gene- 

 ral survey of living things, the untrained student is 

 impressed by the very wide and apparently irrecon- 

 cilable differences in appearance and general charac- 

 ters exhibited by the multitudes of living forms familiar 

 to him. A star-fish and an ox, a butterfly and a fish, 

 an oak and a medusa, seem to differ from one another 

 at least in as great a degree as any one of them dif- 

 fers from a stone, from water, or from air. But, on 

 the other hand, after careful and prolonged study, 

 the student becomes so familiar with the many points 



