4 HISTOLOGY 



cell, while different cells belonging to different forms of life have each 

 their own peculiar proteid or proteids. 



When we realize that these proteids are very changeable and that they 

 go through extensive change upon death, we can understand the diffi- 

 culty of their study and why we know so little about them. 



The questions concerning the exact nature of life lie bound up in pro- 

 toplasm, and but one of them will be commented upon here. Behind 

 these phenomena of life is there any law or principle other than the 

 present known laws of chemistry and physics that is responsible for the 

 manifestations of the life phenomena ? It is our belief that there is, for 

 in no other way can we conceive of the maintenance of so many delicate 

 and variable phenomena for so long a period through so large a number 

 of different conditions. 



That many of the life phenomena can be shown to have a direct 

 sequence to some chemical or physical conditions does not convince 

 that such chemical and physical conditions are the first cause of the 

 phenomena ; and the fact that life is only maintained within certain chemi- 

 cal and physical limits and conditions again does not show that even such 

 conditions are capable of maintaining it for even a short time. The 

 mathematical law of probability and chance would alone convince one 

 of the futility of trying to make matter live for an instant upon such a 

 basis, when so many conditions are constantly interacting and dependent 

 upon one another. As to the nature or origin of such a "vital" law or 

 set of fixed principles, we know nothing. That such a law or laws are 

 supernatural we deny on the ground that any law once established and 

 continued with the probability of permanence in nature is as natural 

 as any of the laws we know about. That this unknown "vital" law is 

 permanent and is subject to rigid continuance without lapse or excep- 

 tion is the only ground on which it can be discussed. We have not even 

 learned enough of its manifestations, as yet, to in any way define it or to 

 classify its results other than to believe that it directs and controls the 

 life processes to ends which vary only with the circumstances under 

 which they exist. 



Protoplasm is protoplasm only so long as it is living. As before 

 mentioned, life must be regarded as a process that is taking place con- 

 stantly in the protoplasm. It is a complicated process which results in 

 constant change and requires a constant supply of new material or food. 

 As a result of this activity, energy is produced in the form of motion, 

 heat, light, and electricity; also many materials are elaborated, as acids, 

 carbohydrates, digestive fluids, protective and supporting materials, 

 poisonous and offensive substances, etc., which are necessary to the exist- 

 ence of the creature to which the protoplasm belongs. 



The dynamic products of protoplasm heat, light, electricity, and 



