96 THE BLOOD. 



of what is most appropriately called the great nutritive fluid. 

 It has been said that all parts are dependent on the blood for 

 nourishment. Those tissues in which the processes of nutri- 

 tion are active are supplied with blood by vessels ; but some 

 less highly organized, like the epidermis, hair, cartilage, etc., 

 which are sometimes called extra-vascular because they are 

 not penetrated by blood-vessels, are none the less dependent 

 upon the fluid under consideration; imbibing, as they do, 

 nourishment from the blood of adjacent parts. 



It must be remembered that in nutrition the tissues 

 are active, selecting, appropriating, and modifying material 

 which is simply furnished by the blood ; and as the real vital 

 force which governs these processes resides in the tissues, ten- 

 dencies of the system, such as the tubercular, scrofulous, or 

 cancerous diatheses, which lead to disordered nutrition, must 

 have their seat in the solids, and not in the circulating fluid. 

 The flrst cause of these conditions may lie in a disordered 

 state of the blood, from bad nourishment, from the introduc- 

 tion of poisons, such as malaria, or the emanations from per- 

 sons affected with contagious diseases, and under some cir- 

 cumstances the elimination of .these poisons may be effected 

 through the blood ; but when they exist in the blood, they 

 either become fixed in the system, or are thrown off. We 

 must regard most of the morbid actions which are dependent 

 on diathesis, as the result of a vice in the tissue itself, not the 

 blood with which it is supplied. It is none the less essential 

 to health, however, that the blood should have its proper 

 constitution. 



The final importance of the blood in the processes of 

 nutrition is evident ; and in animals in which nutrition is 

 active, death is the immediate result of its abstraction in large 

 quantity. Its immediate importance to life can be beauti- 

 fully demonstrated by experiments upon inferior animals. 

 If we take a small dog, introduce a canula through the right 

 jugular vein into the right side of the heart, adapt to it a 

 syringe, and suddenly withdraw a great part of the blood 



