PRESIDENTIAL ADDRESS. 



535 



think of some replacement of one cause by another, and not difficult to adopt 

 such a suggestion, since even in the initial process it was probable that lignt 

 produced its effects subsequent to transformation into some other form of energy 

 such as electricity. In that particular case this idea of forces, and substituted 

 forces, in action, is capable of being formulated in fashion readily understood, 

 because of the ease with which we can think of arrangements in gross parts 

 being determined by such forces. Here in this new case we are, however, think- 

 ing of parts of a different order of magnitude, a fact which I can best illustrate 

 by reference to a single red blood corpuscle occupying a one-tenth millionth of 

 a cubic millimetre, and containing in a one-hundredth part of that space as many 

 molecules of hemoglobin as there are present red blood corpuscles in one cubic 

 millimetre of blood— that is to say, five millions. 



Now there is in reality no difficulty in considering some electrical agency 

 as limited in its action to the minute dimensions in which each pigment-forming 

 reaction is in process ; some electrical machine such as, for example, might be 

 energised by electrons derived from the dissolved molecules of a pigment-salt ; 

 such" a machine as might be capable of transforming both light and heat into 

 electrical energy, and which would maintain a process in the absence of light 

 at the cost of energy obtained in the form of heat. 



When thinking of the persistence of such reactions as this, initiated in this 

 way by the action of certain primary causes that are then subsequently removed 

 without any cessation of the reaction, we are concerned with one of the funda- 

 mental properties of living matter. Everywhere in living matter numerous 

 instances of this property are being discovered, as in the study of immunity and 

 of protection from infection. Nor is there reason to believe that this persistent 

 quality of such variations will not finally be explained in terms of physical 

 chemistry. The main characteristic of living matter is that it contains machines 

 formed by electrolytes distributed upon the complex surfaces of matter in a 

 state of colloidal solution, and in the presence of competitive solvents, and that 

 such machines are multiplied within it. Some of these mechanisms are arranged 

 and perfected by the action of physical conditions operative on the surface of 

 living matter, as, for instance, light. Some by energy derived from internal 

 sources, but in a form that embodies conditions originally derived from the 

 surface. Some are primarily due to internal disturbances in the equilibrium 

 of these complex solutions produced by those chemical reactions which take place 

 there. 



Now, returning to the grosser characteristics of blood, we find it possessed 

 of other characters curiously reminiscent of the surface of the body, and especially 

 of glandular invaginations ' from the surface. Thus it is everywhere confined by 

 cells spread upon its surface, the endothelium, which limit its relationship to 

 the general mass of the interior. Its new-formed cells are again passed into an 

 internal core covered by these surface cells, and from this situation, except as a 

 result of violence, they* do not pass. We might, in fact, compare the blood with 

 a gland in which the' red blood corpuscles were seen as a secretion occupying 

 a lumen which represents the original external surface of the body. I do not 

 wish to lay any emphasis on this point except in so far as it renders clearer this 

 thought : that blood covered by its endothelium represents a single tissue which 

 ten^s. like any gland, to grow into every interstice of the body, where the 

 conditions of mechanical pressure permit. I shall render the point clearer by 

 saying that the blood capillaries are no more and no less than blood-tissue. 



In its early days this blood-tissue, or, if you will, this capillary network, is 

 pushed into each portion of the body by pressure due to its growth. In its 

 later stage, the tissues surrounding it which form the muscular coat of the heart 

 and the walls of the blood-vessels are arranged into an external mechnnical 

 system providing a new pressure, which still further tends to push the blood- 

 tissue into every available space, a process such as, for example, takes place in 

 tumniir development and in the granulation tissue present in wounds. 



It is a general postulate that cells long exposed to constant conditions may 

 come to be stamped by those conditions. Special change takes place from the 

 time when the blood grew onward by pressure of its own growth to the time when 

 this movement is more clearly determined by the mechanism of the circulatory 

 system, and divergent results occur in different localities of the blood -tissues 



