130 PHYSIOLOGY CHAP. 



acid least of all, since, as will be shown later on, the greater part 

 at any rate is formed by a synthetic process in the kidneys. 

 Under pathological conditions, however, when the renal function 

 is profoundly affected or abolished (uraemia), as also in grave 

 alterations of the blood (leucaemia), besides these nitrogenous 

 products others, which are normally present in the urine in 

 exceedingly small quantities, e.g. the xanthine bases (Scherer), can 

 be demonstrated in the serum. 



IV. Besides the nitrogenous compounds, neutral fats are found 

 in the blood serum, emulsified to minute drops which can readily 

 be extracted with ether. The amount, which under normal con- 

 ditions does not exceed G'l-0'2 per cent, increases conspicuously 

 after a fatty meal, giving a milky appearance to the serum, and 

 it may reach or exceed 1 per cent of the total quantity of blood 

 (Kohrig) ; whereas in the fasting state only minute traces remain 

 (Pfeiffer). It is thus obvious that the fats of the blood are derived 

 principally from the fatty substances taken in with the food. In 

 certain morbid conditions, however (alcoholism, diabetes, diseases 

 of the bone marrow), the amount of fat in the blood plasma may 

 increase so much that the serum assumes a milky aspect (lipaeniia) 

 as after a meal that has been rich in fats. It is therefore probable 

 that the fat of the blood is, even under normal conditions, derived 

 to a lesser extent from what is eliminated or liquefied from the 

 adipose tissues. 



In addition to neutral fats, blood serum contains soaps, 

 lecithin, and cholesterin (Hoppe-Seyler). These form part of the 

 products of pancreatic digestion, hence they also come in part 

 from the digestive canal. 



A third group of organic substances also found in serum are 

 conventionally comprised under the term carbohydrates : glucose, 

 glycogen, lactic acid. There is yet another reducing substance, 

 which is not fermentable ; it contains phosphorus, is capable of 

 extraction with ether, and gives all the reactions of jecorin 

 (Jacobson). Lastly, there is a small quantity of animal gum 

 (Freund). 



The most important of all these substances is certainly glucose, 

 which originates partly direct from the food, partly from the 

 digestive transformation of alimentary starch, partly from the 

 glycogen of the liver and muscles. The quantity of glucose in 

 the blood is independent of the nature of the food, because, as we 

 shall see later, nearly all the glucose absorbed from the intestine 

 is stored up in the liver in the form of glycogen (liver starch). 

 The amount of glucose found in normal human blood varies from 

 010 to 0*15 per cent (Otto); but under abnormal conditions it 

 may reach 0*3 per cent or more. It is at a maximum during post- 

 digestive absorption in the blood of the portal veins, while during 

 inanition it is most abundant in the blood of the hepatic veins. 



