THE PLASMA 155 



Besides the proteids we find in the blood: fats (and the cholesterin ester 

 of fatty acids, but as a rule no free cholesterin, Hiirthle) ; glycerin and carbo- 

 hydrates (sugar, probably for the most part in combination with lecithin as 

 jecorin: Jacobsen, Henriques, Bing) ; also substances which are formed in the 

 activity of the tissues and either represent decomposition products to be given 

 off from the body (like urea, uric acid, creatin, carbamic acid, paralactic acid, 

 hippuric acid, etc.) or are formed for the purpose of influencing the functions 

 of different organs (internal secretions, cf. Chapter XI) in short, everything 

 which the tissues have need of for their activity, and most of the products 

 arising from this activity. 



With the exception always of the proteids, these substances occur in very 

 small quantities in the blood. In the intervals of digestion one finds from one 

 to seven per cent of fat in the serum, while during digestion it mounts much 

 higher. Even in starvation (one hundred and twenty hours after food has been 

 taken) the fat content of the blood is higher than in the inanitiate condition 

 (twelve hours after the last meal) a fact connected with the movement of the 

 body's fat for the purpose of covering the food requirements (Schulz). In the 

 healthy condition the sugar content of the serum amounts to about 1-1.5 per 

 cent, but after very abundant feeding of carbohydrates may increase to three 

 per cent and higher. The maximum urea content is about one per cent, etc. 

 These quantities appear at first sight to be astonishingly small, but they become 

 intelligible when we reflect that the blood is in continual motion and its con- 

 tributions of fat and carbohydrates to all the tissues are continually being 

 replaced from the great storehouses of the body. In the same way it takes up 

 the decomposition products from the tissues, and continually eliminates them 

 by way of the excretory organ so that under normal conditions it contains at 

 any given time a very small quantity of these substances also. 



Various enzymes have been demonstrated in the blood. Thus according 

 to Michaelis and Cohnstein, there is an enzyme which in the presence of 

 red blood corpuscles and oxygen destroys fat (lipolytic enzyme). Arthus has 

 found an enzyme which splits monobutyrin into glycerin and butyric acid; 

 but an enzyme which would split neutral fat has not been certainly demon- 

 strated. Further, a diastatic enzyme which changes starch into maltose, one 

 changing the latter into dextrose, and an enzyme by which sugar is destroyed 

 (glycolytic enzyme), are said to be present. Hedin mentions a feeble enzyme 

 which digests proteid in an alkaline medium. 



Likewise there are found in the blood substances which act against the 

 enzymes peculiar to the body, represent therefore antienzymes, and develop 

 antipeptic, antitryptic, and antichymotic effects. 



Serum contains moreover certain substances which have the power to kill 

 Bacteria and foreign cells generally. The serum of one animal species destroys 

 the blood corpuscles of another species, if the species are not very closely 

 related a fact which explains, in part at least, the harmful effects of a 

 transfusion of foreign blood. This globulicidal action, as it is called, as well 

 as bactericidal action of the blood is very different in different genera of 

 animals. Thus the serum of horse's blood is only slightly poisonous to man 

 and is tolerated in pretty large doses. The serum of human blood exercises 

 a powerful effect on the typhoid and cholera bacteria, while on the pus- 



