322 THE BLOOD. 



amount, however, is subject to great variations. As a general rule, 

 traces only are found, but it may increase at times to 1.5G per cent., 

 as calculated for the blood as a whole. Larger amounts are seen 

 under pathological conditions. 



Fat is normally found to the extent of from 0.2 to 0.3 per cent., 

 but may be greatly increased by the ingestion of much fatty food, 

 as also in various pathological conditions. 



Urea is likewise found in only very small amounts under normal 

 conditions (0.016 to 0.020 per cent.), while in disease much greater 

 quantities may be encountered. Ammonia is said to be present in 

 normal blood to the amount of 0.001 per cent. 



The further occurrence in the blood of soaps, cholesterin, and 

 lecithins, as also of uric acid, kreatin, carbaminic acid, paralactic 

 acid, hippuric acid, etc., has been mentioned. All these bodies are 

 found in only extremely small amounts, and need not be con- 

 sidered at this place. The pathological constituents of blood, such 

 as leucin, tyrosin, acetone, bilirubin, etc., will be considered in future 

 chapters. 



Of gases, finally, we find in the plasma and serum small amounts 

 of nitrogen and oxygen, which are present simply in solution, and 

 somewhat larger amounts of carbon dioxide, which in part at least 

 is more or less firmly combined with albumins. 



The Leucocytes. 



The morphological characteristics and general chemical composi- 

 tion of the leucocytes have already been considered (see pages 303 

 and 306). At this place I wish merely to draw attention to one 

 substance which, according to Lilienfeld, is found in special 

 abundance in the nuclei of these bodies, and which has been termed 

 nucleohiston. 



Nucleohiston. This substance was first isolated by Kossel and 

 Lilienfeld from the thymus gland of the calf, but has since been 

 obtained from the leucocytes of the lymph-glands, as also from the 

 splenic cells, the testicular cells, the spermatozoa, and from the 

 epithelial lining of the small intestine. In all probability it repre- 

 sents an important constituent of all cellular nuclei. 



Isolation. Nucleohiston is most conveniently obtained from the 

 leucocytes of the thymus gland. To this end, the gland is carefully 

 dissected free from fat and all larger bloodvessels, and finely hashed. 

 This mass is extracted with cold water, passed through muslin, and 

 centrifugalized. The aqueous extract is further filtered, and the 

 nucleohiston precipitated by the careful addition of dilute acetic 

 acid. It is filtered off, dissolved in water with the aid of a small 

 amount of a dilute solution of sodium carbonate, reprecipitated 

 with acetic acid, and purified by a repetition of this process. It is 

 then washed with acetic water, extracted with alcohol and ether, 

 and finally dried at a temperature of from 110 to 115 C. 



