THE BLOOD. 109 



spleen and in the lymphatic glands; they appear in great 

 numbers immediately after eating, and quickly disappear 

 again. Thus, a German observer (Hirt) computed the pro- 

 portion of white to red corpuscles in his own blood, and 

 found that before breakfast it was 1 in 1800, an hour after- 

 wards 1 in 700, and between eleven and twelve o'clock 1 in 

 1500. He took dinner at one o'clock, after which the pro- 

 portion was 1 in 400, while two hours afterwards it sunk to 

 1 in 1475. After an eight o'clock supper it was 1 in 550, 

 and at eleven o'clock 1 in 1200. 



78. Turning now to the chemical composition of the blood, 

 we find that the liquor sanguinis is essentially an albuminoid 

 solution. It is slightly alkaline, and contains about 97 parts 

 of solid matter in every thousand. Of these only four parts 

 consist of fibrin ; while the albumen, which is the principal 

 constituent of the serum, forms nearly 79 parts ; the mineral 

 matters constitute more than 8 parts ; urea, kreatin, and 

 other matters soluble in water, usually grouped together 

 under the name of extractive, make up about 4, and the fats 

 less than 2 parts in the thousand. 



The blood is, in health, very uniform in its composition, 

 and it will naturally occur to ask how the uniformity is 

 maintained, seeing that the additions made to it must vary 

 much with the character of the diet. It may also be asked 

 how it happens that the blood, which nourishes the whole 

 body, has so little resemblance to the total composition of the 

 body. Both these questions admit of one answer, namely, 

 that the amount of any substance in the blood at one time 

 depends not only on the quantity which enters the circulation, 

 but on the length of time that it remains there. Thus, there 

 is very little fatty matter in the blood, although quantities 

 enter with the supplies of nourishment from the food, and at 

 least one substance, roughly classed under this head, choles- 

 terine, is returned from the brain ; and there is only a very 

 minute quantity of urea in the blood, although there is 

 reason to believe that a considerable amount of what is 

 eliminated by the kidneys pre-exists in it : but the explana- 

 tion is simply that none of these substances are allowed to 

 accumulate in the blood, that they are removed from it as 

 speedily as they enter it. 



