THEIR CAUSES, NATURE, AND PREVENTION. 17 1 



process brought about not by the existence, as was once sup- 

 posed, of fibrin as fibrin in the blood, but by the action of a 

 ferment upon two substances pre-existent in that fluid, known 

 as Jibrinogen and fibrinoijlastin. 



The second problem we have to consider is the means by 

 tvhich the vitality of the blood is Tnaintained. 



I have already said that the source of the blood is the alimen- 

 tary matter we ingest or take into our stomach and bowels in 

 the ordinary processes of eating and drinking, and again I repeat 

 that in order for the preservation of the equilibrium in the 

 different constituents of the blood, the ingested matter must 

 contain all the elements, and that too in due proportion, neces- 

 sary for their supply. In other words, the food must contain a 

 due proportion of flesh-forming matter, of heat producers, of 

 alkaline salts (potash and soda), iron, phosphorus or phosphoric 

 acid, magnesia and lime ; with a few other elements of a less 

 important character, such as sulphur. Before considering the 

 effects of improper alimentation in the direction of inducing 

 diseased processes it will be useful to glance briefly at the 

 effects of adverse agencies on the blood itself. Looking at the 

 blood in the light of its vast importance in the animal economy, 

 it would seem at first sight that it ought to be a stable tissue. 

 Nothing, however, is further from the truth than is such a 

 supposition, as even quantitative deficiencies or excesses in its 

 elements are sufficient to induce grave changes, both structurally 

 (histologically) and functionally (physiologically) ; thus, if water 

 is deficient in quantity the blood becomes thick, its plasticity is 

 increased, and, as a consequence, there is a great tendency to 

 stagnation (congestion). If water is superabundant the colloids 

 are held in an undue state of solution, the colouring matter is 

 dissolved out of the red cells, and the walls of these little bodies 

 may be actually broken up or disintegrated. Not only is this 

 the case, but, owing to the macerating process to which they 

 are subjected, the white cells are injuriously acted upon, and 

 the elements entering into the composition of the walls of the 

 blood-vessels (particularly of the capillaries) become weakened, 

 and their vitality lowered and they allow of the easy escape 

 of serum into the tissues and cavities of the body, and thus we 

 have produced dro2:)sies (effusions). It is a well-known fact, too, 

 that an excessive draught of cold water when the system is 

 heated, will, particularly in man, determine an attack of nettle- 

 rash solely by its effects on the blood and the glands ; and 

 more than this, repletion and congestion of important organs is 

 frequently produced by similar causes. 



The colloids (proteids) of the blood are absolutely necessary, 

 not only for the building up of the muscular and other tissues, 

 but for their ordinary repair, as well as for the restoration and 



