5 1 4 THE POPULAR SCIENCE MONTHLY. 



ical constituents of foods, become necessary to liberate their need- 

 ed supplies of energy. 



As all the food constituents contribute to the blood-making 

 processes, they all in like manner through digestive disintegration 

 contribute to the supplies of energy required in the animal econ- 

 omy. The energy provided in foods in the potential form is quite 

 as important in building animal tissues as the chemical elements 

 entering into their composition, as when liberated in the form of 

 heat it is utilized in constructive metabolism and stored again as 

 potential energy in the animal tissues formed. The destructive 

 metabolism taking place in these tissues, as an essential concomi- 

 tant of their vital activities, again liberates energy in the form of 

 heat, which, with that derived from the digestion of foods, is used, 

 so far as needed, in the reconstructive process, and the balance 

 appears as animal heat. 



We have noticed the recently discovered continuity of the 

 protoplasm of plants, but we can not fairly infer that there is a 

 similar continuity of the protoplasm of the higher animals that 

 have a highly specialized nervous system which brings the dif- 

 ferent organs and functions into harmonious action more com- 

 pletely and efficiently than they could be by simple threads of 

 protoplasm like those which unite the cells of plants. The widely 

 different products of destructive metabolism in the various tissues 

 of plants and animals, aside from other considerations, furnish 

 conclusive evidence that while the general role of protoplasm is 

 everywhere the same, it must differ materially in composition and 

 constitution in the different conditions in which it is found. As 

 stated by Dr. Foster, " It is obvious that the varieties of proto- 

 plasm are numerous, indeed almost innumerable. The muscular 

 protoplasm which brings forth a contractile katastate must differ 

 in nature, in composition that is, in construction from glandu- 

 lar protoplasm whose katastate is a mother of ferment. Further, 

 the protoplasm of the swiftly contracting striped muscular fiber 

 must differ from that of the torpid, smooth, unstriated fiber ; the 

 protoplasm of human muscle must differ from that of a sheep or 

 frog ; the protoplasm of one muscle must differ from that of an- 

 other muscle in the same kind of animal, and the protoplasm of 

 Smith's biceps must differ from that of Jones's." 



What determines these differences and gives direction to such 

 diverse metabolic activities? Chemical and physical considera- 

 tions fail to clear up the mystery of life and its varied manifesta- 

 tions. We may look upon protoplasm as the physical basis of 

 life, and consider vital activities as resulting from its inherent 

 properties ; but this does not aid us in gaining a better knowledge 

 of the mysterious endowments of living matter. What gives rise 

 to these diverse properties in different species and in different 



