540 OF THE CIRCULATION OF BLOOD. 



the brain becomes inactive, and stupor ensues ; the medulla is torpid, and the 

 powers of respiration and excretion are imperfect: voluntary motion is almost 

 suspended ; secretions fail ; molecular nutrition ceases ; and at a rate much 

 more early than in other modes of death, molecular death follows close on 

 somatic death, that is, structures die and begin to run into decomposition as 

 soon as the pulse and breath have ceased ; nay, a partial change of this kind 

 may even precede the death of the whole body; and parts running into gan- 

 grene, as in the carbuncle of plague, the sphacelous throat of malignant scarla- 

 tina, and the sloughy sores of the worst forms of typhus, or the putrid odour 

 exhaled even before death by the bodies of those who are the victims of simi- 

 lar pestilential disease, are so many proofs of the early triumph of dead over 

 vital chemistry." "The appearance of petechiae and vibices on the external 

 surface, the occurrence of more extensive hemorrhage in internal parts, the 

 general fluidity of the blood, and frequently its unusually dark or otherwise 

 altered aspect, its poisonous properties as exhibited in its deleterious operation 

 on other animals, and its proneness to pass into decomposition, point out the 

 Blood as the first seat of disorder; and by the failure of its natural properties 

 and offices as the vivifier of all structure and function, it is plainly the medium 

 by which death begins in the body." 



CHAPTER XII. 



OF THE CIRCULATION OF BLOOD. 



1. Of the Circulation in General. 



709. THE Circulation of nutritive fluid through the body has for its object, 

 on the one part, to convey to every portion of the organism the materials for 

 its growth and renovation, together with the supply of Oxygen which is re- 

 quisite for its vital actions, especially those of the Muscular and Nervous 

 systems ; and at the same time to carry off the particles, which are set free by 

 the disintegration or waste of the tissues, and which are to be removed from 

 the body by the Excreting processes. Of these processes, the one most con- 

 stantly in operation, as well as most necessary for the maintenance of the 

 purity of the blood, is the extrication of Carbonic acid, through the Respira- 

 tory organs; and this is made subservient to the introduction of Oxygen into 

 the system. The extent, therefore, to which a Circulating apparatus is de- 

 veloped in the Animal kingdom, is partly dependent upon the degree in which 

 the function of nutritive Absorption is limited to one part of the body; and 

 partly upon the arrangement of the Excreting surfaces, and especially of the 

 Respiratory apparatus. Where the Digestive cavity extends itself through 

 the whole system, so that every part can absorb at once from its parietes, 

 and where the whole external surface is adapted, by its softness and permeability, 

 to expose the fluids of the body to the aerating medium around, there is no 

 necessity for any transmission of fluid from one part to another; and accord- 

 ingly, in the lowest animals, which are thus formed, no true Circulation exists. 

 Again, in the Insect tribes, in whose bodies the absorption of fluids can only 

 take place at fixed points, there is a Circulation, for the purpose of transmit- 

 ting the absorbed matter to the remote portions of the body; but as every part 

 of the interior is permeated by air, the second of the above-named purposes 



