ANATOMICAL ELEMENTS. 5 



ticularly the salivary glands, he found the blood red in the veins during 

 secretion, but becoming dark as soon as secretion was arrested. In the sub- 

 maxillary gland, by Faradization of a certain nerve, called the motor nerve of 

 the gland, Bernard was able to produce secretion, and by stimulating another 

 nerve, to arrest it ; in this way changing at will the color of the blood in the 

 vein. It was found by the same observer that division of the sympathetic in 

 the neck, which dilates the vessels and increases the supply of blood to one 

 side of the head, produced a red color of the blood in the jugular. He also 

 found that paralysis of a member by division of the nerve had the same 

 effect on the blood returning by the veins. 



The explanation of these facts is evident in view of the reasons why the 

 blood is red in the arteries and dark in the veins. Its red color depends upon 

 the presence of oxygen in the corpuscles ; and as the blood passes through 

 the lungs it loses carbon dioxide and the corpuscles gain oxygen, changing 

 from black to red. In its passage through the capillaries of the system, in 

 the ordinary processes of nutrition, the blood loses oxygen and gains carbon 

 dioxide, changing from red to black. During the intervals of secretion, the 

 glands receive just enough blood for their nutrition, and the ordinary inter- 

 change of gases takes place, with the consequent change of color ; but dur- 

 ing secretion, the blood is supplied to the glands in greatly increased quan- 

 tity. Under these conditions, it does not lose oxygen and gain carbon 

 dioxide in any great quantity, as has been demonstrated by actual analysis, 

 and consequently there is no marked change in color. When filaments of 

 the sympathetic are 'divided, the blood-vessels are dilated, and the supply of 

 blood is increased to such an extent that a certain proportion passes through 

 without parting with its oxygen a fact which has also been demonstrated 

 by analysis and consequently it retains its red color. The explanation in 

 cases of syncope is probably the same, although this is merely a supposition, 

 Even during secretion, a certain quantity of carbon dioxide is formed in the 

 gland, which, according to Bernard, is carried off in solution in the secreted 

 fluid. 



It may be stated, then, in general terms, that the color of the blood in the 

 arteries is bright red ; and in the ordinary veins, like the cutaneous or mus- 

 cular, it is dark blue, almost black. It is red in the veins coming from glands 

 during secretion, and dark during the intervals of secretion. 



ANATOMICAL ELEMENTS IN THE BLOOD. 



In 1661, Malpighi, in examining the blood of the hedgehog, with the im- 

 perfect lenses at his command, discovered little floating particles which he 

 mistook for granules of fat, but which were the blood-corpuscles. He did 

 not extend his observations in this* direction ; but a few years later (1673), 

 Leeuwenhoek, by the aid of simple lenses of his own construction, ranging in 

 magnifying power between forty and one hundred and sixty diameters, first 

 saw the corpuscles of human blood, which he minutely described in a paper 

 published in the Philosophical Transactions, in 1674. To Leeuwenhoek is 

 generally ascribed the honor of the discovery of the blood-corpuscles. About 



